Introduction

Marine pollution is a global environmental threat where human activities largely contribute to the discharge of various emerging contaminants into marine ecosystems. Two important classes of contaminants are toxic metals and microplastics1,2. Toxic metals are naturally found in the earth’s crust and are considered trace elements if their concentrations are in the ppb to low ppm range (10 ppm). According to the World Health Organization, toxic metals are classified as physiologically essential elements (Zn, Se, Fe, Cu, Cr and Mo) and non-essential elements with no physiologically relevant role (Hg, Pb and Cd)3. Elevated levels of trace metals can arise from natural phenomena such as volcanic eruptions, rock weathering; and from human activities such as mining and combustion of fossil fuels4. The release of agricultural, industrial, electronic, and household waste, along with the use of pesticides containing toxic metal salts contributes to increased concentrations of toxic metals5,6. Toxic metals have the potential to accumulate within the aquatic ecosystem thereby affecting the quality of seawater and subsequently poisoning risks to human health such as neurological disorders, carcinogenic effects, and skeletal weakness7. Metals usually have low solubility in water and are mostly adsorbed to the solid phase thereby ending up mostly on sediments. Once released in the marine environment, they undergo various physicochemical processes that influence their spreading between particulate matter or dissolved phase. The free ionic metal undergoes a solvation process leading to the formation of complexes with inorganic ligands like carbonates, chlorides, nitrates, and hydroxides. This complexation activity is dependent on different parameters such as pH, salinity, redox potential, temperature, and the quantity of ligands available8.

Phthalates are plasticizers present in a widespread range of plastic products to improve plasticity, transparency, robustness, and longevity9. Phthalates are also used as solvents and additives in adhesives, printing inks10, toys, food packaging, personal care products, cosmetics, and building materials11,12. Despite their widespread use, there have been concerns about potential negative health effects, leading to efforts in reducing their use in consumer products13. Phthalates are non-halogenated esters of phthalic acid classified into low-molecular-weight (LMW) and high-molecular-weight (HMW)14. LMW phthalates, such as diethyl phthalate (DEP) and dibutyl phthalate (DBP), are volatile and have a low viscosity, making them suitable for use in products such as perfumes and hairsprays9. HMW phthalates, such as di-2-ethylhexyl phthalate (DEHP) and diisononyl phthalate (DiNP), have a higher viscosity and are used as plasticizers in materials such as vinyl flooring and inflatable products. All phthalates have a linear structure and are characterized by the presence of two ester groups attached to a central carbon atom15. Their solubility in water decreases as the length of the side chain increases. Phthalates are also known for their ability to interact with proteins and other biomolecules16, which has led to concerns about potential impact on human health. While a part of the plastic waste is being properly disposed of, millions of tons are continuously released into the environment in aqueous media and thereby induce a noticeable influence on the ecological system17,18,19,20,21. Exposure to phthalates occurs through air, soil, water, or food and enter the body through ingestion, inhalation and through skin contact. Phthalates are known as endocrine disruptors leading to cancer, reproductive/fertility problems, asthma, and lung disorder22,23. In marine environments, toxic metals can persist for long periods due to their low solubility in water, which results in their adsorption onto sediments. This means that even once metals are deposited on the seabed, they remain available for uptake by marine organisms, potentially causing long-term exposure. Many of these metals are highly toxic, even at low concentrations, and have been shown to affect marine life in multiple ways7. For example, mercury can accumulate in fish tissues, leading to methylmercury formation, a compound that is particularly harmful to human health through seafood consumption. Similarly, arsenic and cadmium can cause neurological damage and reproductive issues in marine organisms. The ecological impact of these metals is significant, as they can interfere with cellular processes, impair growth, disrupt immune function, and reduce reproductive success in marine species. Additionally, their ability to biomagnify through the food chain poses substantial risks to both marine organisms and humans who rely on seafood as a food source. Similarly, phthalates pose significant threats in marine ecosystems to both ecological health and human wellbeing. These chemicals interfere with the hormonal systems of both aquatic organisms and humans22,23. In marine life, exposure to phthalates has been linked to altered growth, reproductive abnormalities, and developmental issues. For example, fish exposed to phthalates may experience hormonal imbalances that affect fertility and sexual differentiation. The persistence of phthalates in marine environments, often leaching from plastics over time, exacerbates their potential for ecological harm. The prevalence of both toxic metals and phthalates in marine environments has been well documented globally, but studies focused on specific regions such as the Mediterranean, including Lebanon, remain limited. The Mediterranean Sea is highly susceptible to contamination due to its unique hydrological conditions, including limited water exchange with other seas, which results in slower dispersion of pollutants. Industrial activities, shipping, agriculture, and urbanization along the Mediterranean coast contribute significant amounts of contaminants to the sea, leading to localized hotspots of pollution. For example, elevated concentrations of toxic metals such as lead and mercury have been recorded in sediments and marine organisms near coastal industrial zones.

The Mediterranean Sea is vulnerable to contamination due to its unique hydrological and geographical characteristics24 including chemical contaminants from industrial, agricultural, and urban sources25,26. Lebanon is a small Mediterranean country with a coastline that spans over 225 km and accommodates around 2.6 million people constituting 70% of the population27. The majority of Lebanon’s economic activity is focused around this coastal zone, which accounts for approximately 75% of the national GDP, has active transport-export-transit services and is a popular tourist destination28. Concerns about the effects of emerging contaminants on the aquatic ecosystem are growing with the increasing economic affliction and public health hazards. Lebanon’s shoreline is heavily contaminated, where the coastal ecosystem diversity is vulnerable to three main potential hazardous threats: oil spills, chemical contaminants, and fragmentation of natural habitats29. Notably, the Lebanese maritime water is exposed to major contamination sources, such as high shipping traffic, agricultural runoffs, industrial wastewater effluents, sewage outfalls, oil spills, and leachates from beachfront landfills mainly due to the presence of solid waste dump sites and major industries directly on the Lebanese Coast30,31. These sources discharge roughly 950,000 m3 of effluent directly into the sea each day. Furthermore, approximately 60% of Lebanon’s sewage is discharged into the sea28. In terms of solid waste disposal sites, eight large coastal dumpsites have been identified. Although several projects have been conducted to decipher marine water contamination levels of toxic metals in Lebanon, current literature is scarce and limited to certain areas or freshwater sources due to the lack of comprehensive research along the Lebanese coast. Our study aims to assess the levels of toxic metals and phthalate contamination in seawater and sediments along the Lebanese Mediterranean coast, identify contaminated hotspots, and evaluate the potential anthropogenic impacts on marine ecosystems. Using rigorous data collection and subsequent statistical analyses, this case study reports the concentration levels of toxic metals and phthalates in seawater and sediments along the Lebanese coast from 40 different locations, thus providing a detailed understanding of the distribution of these pollutants.

Materials and methods

Sampling

Seawater and sediment samples were collected from 40 distinct locations along the Lebanese Mediterranean coast on July 4, 5, and 6, 2022 using acid-washed plastic bottles specifically for toxic metal analysis and brown glass bottles for phthalate analysis. The selected sampling locations are representative of the study area, such as potential pollution sources or less disturbed sites. From every location, water samples were collected in triplicates from the surface, ensuring minimal disturbance to the surface layer. Bottles were filled to 80% capacity to allow for air expansion. After collection, all samples were stored at 4 °C to prevent any alteration of their chemical composition. Seawater samples were then filtered through precleaned funnel filters to remove particulate matter prior to analysis. To sample sediment, a representative site along the waterbody was chosen, avoiding areas with visible contamination or disturbance. A hand trowel was used to collect sediment samples from the surface layer, typically at a depth of 0–10 cm, to capture the most recent sediment deposits. Sediments samples were collected in triplicates. The rocky terrain at certain sampling locations (specifically sites 7, 10, 11, 12, 16, 18, 21, 23, 24, 25, and 32) limited the ability to gather sediment samples, necessitating the use of seawater samples from these sites only. The map represented in Supplementary Fig. 1 reports the sampling sites covering the whole Lebanese coast of the Mediterranean Sea. Supplementary Table 1 reports the corresponding GPS coordinates and hotspots.

Reagents and sample preparation

The used reagents were of high purity and high analytical grade: ethyl acetate and dichloromethane were purchased from Fischer Scientific (Schwerte, Germany); 30% Hydrogen peroxide solution (Sigma Aldrich, Germany), 69% Nitric acid (BDH Laboratory supplies, England), 37%Hydrochloric acid (AnalaR Normapur, France). The toxic metal standard solutions As, Cd, Co, Cr, Cu, Fe, Hg, Mo, Mn, Ni, Se, Sn, Pb, and Zn were purchased from Merck (Darmstadt, Germany). The phthalate standards Dimethyl phthalate (DMP), Diethyl phthalate (DEP), Diallyl phthalate (DAP), Diisobutyl phthalate (DiBP), Di-n-butyl phthalate (DBP), Dipentyl phthalate (DPeP), Di-hexylphthalate (DHxP), Benzyl butyl phthalate (BBP), Dicyclohexyl phthalate (DHCP), Di(2-ethylhexyl) phthalate (DEHP), Di(2-propylheptyl) phthalate (DPHP), Di(n-octyl) phthalate (DnOP), dibenzyl phthalate (DBzP), and the deuterated phthalates DMP-d4, DEP-d4, DiBP-d4, DBP-d4, DpeP-d4, DHxP-d4, DCHP-d4, DEHP-d4, and DBzP-d4 were purchased from Santa Cruz Biotechnology (Heidelberg, Germany). Stock solutions of 50 ppm were prepared for each of the phthalates as well as mixtures of these phthalates at different concentrations. To validate the accuracy of the method, we purchased certified reference materials for salt water (ERM-CA403) and for wastewater (ERM-CA713) from the Institute for Reference Materials and Measurements (Geel, Belgium). All solutions were prepared with analytical reagent grade chemicals and ultrapure water (18 MΩ.cm, 25 °C, Total Organic Carbon content < 2 ppb) by purifying distilled water using a Milli-Q water purification system (Millipore S.A., St Quentin-en-Yvelines, France). Analytical grade water was used in the toxic metal analysis. For each sample, triplicates were analyzed to ensure the reliability and accuracy of the results. Each sample was divided into three separate aliquots, allowing for independent measurements of the same sample under identical conditions. This approach minimizes the impact of any random variability and provides a more robust statistical representation of the data.

Sample digestion for toxic metal analysis

The extraction of toxic metals from the seawater samples involved acid digestion following EPA Method 3015A32 with Multiwave ECO microwave digestion system (Anton Paar GmbH, Graz, Austria) equipped with 16 pressure-activated-venting vessels (Rotor 24HVT50, Anton Paar GmbH, Graz, Austria). A reaction vessel was used to combine 22.5 ml of the water sample with 2 ml of concentrated HNO3 and 0.5 ml of concentrated HCl. Sample digestion was performed at (1) 850 W at 170˚C for 10 min with a ramp of 150C/min and (2) 850 W at 170˚ C for 22 min followed by cooling (Supplementary Table 2). Samples were then transferred into 50 mL falcon tubes, diluted 5 times with 3% HNO3 prepared with ultrapure deionized water and were stored at 4˚C until analysis.

ICP-MS analysis

By adapting EPA Method 200.833, we performed elemental analysis using the Inductively Coupled Plasma Mass Spectrometer (ICP-MS) iCAP Q / iCAP RQ ICP-MS (Thermo Fisher Scientific Inc., Bremen, Germany) operating with argon gas of spectral purity (99.9995%). The instrument was tuned using iCAP Q/RQ TUNE aqueous multi-element standard solution in 2% HNO3 + 0.5% HCl solution (Thermo scientific, Bremen, Germany) before each experiment. The optimal parameters for the torch position, ion lenses, gas output, resolution axis (10% of peak height) and background (< 20 shots) were obtained with the tuning solution (1 mg/L), to maximize ion signals and to minimize interference effects due to high oxide levels (Supplementary Table 2). Each sample was measured 3 times and the quantification of the toxic metals was carried out using external calibration curves. Standard solutions were prepared in 3% nitric acid, and for each element, the external calibration curve was plotted using several concentrations (Supplementary Fig. 2). The correlation coefficients across all calibration curves demonstrate a strong linear relationship across the studied concentration ranges. Utilizing full quantitative mode analysis, multiple isotopes of the elements were measured, and isotopic ratios in digested samples were examined to ensure the absence of polyatomic interferences. Certified reference materials (seawater and wastewater) were employed to ascertain method accuracy where the recovery percentages of the metals were in the range of 81.67 to 117.61% for seawater and 81.13 to 116.75% for wastewater (Supplementary Table 3). The Limit of Detection (LOD) and Limit of Quantification (LOQ) were calculated using the standard deviation of blank measurements (σ) and the slope (S) of the calibration curve, based on established protocols34. Blanks were analyzed to determine σ, and a calibration curve was constructed using standard solutions to calculate S. The calculated LOD and LOQ were validated by analyzing low-concentration samples to confirm their accuracy35. The LOD for each element was determined through blank determination assays, equivalent to three times the standard deviation of 20 blank replicates36. The LOQ was calculated as twice the LOD for each element. Precision for toxic metal analysis via ICP-MS was validated through spiking methodology at various concentrations within permissible limits for each matrix, with recovery percentages calculated for each metal. Each sample’s data was collected twice, with toxic metal content measured in triplicate, and average values reported. The investigation encompassed toxic metals As, Cd, Co, Cr, Cu, Fe, Hg, Mo, Mn, Ni, Se, Sn, Pb, and Zn. Standard solutions of the 14 toxic metals were prepared as stock solutions with initial concentrations of 1000 ppm before dilution in 3% HNO3 to generate a range of concentrations from 3 ppm to 0.05 ppb prior to analysis.

Sample preparation for GC–MS analysis

The samples of the filtered water were treated with sulfuric acid to stop biological activity. Solid Phase Extraction was optimized from EPA method 3535A37 and an adopted method of extraction to perform large-scale analysis efficiently with minimal contamination and improved recoveries38, in brief, CHROMABOND SPE vacuum manifold (Macherey–Nagel, Düren, Germany) was used with 24 WELCHROM C18E 6 mL, 500 mg, glass cartridges (Welch Materials, Connecticut, United States). Prior to sample extraction, the cartridges were cleaned three times with 5 mL acetone and 5 mL dichloromethane alternatively and conditioned with 5 mL ethyl acetate, 5 mL acetone, and 5 mL ultrapure water. After percolation, the cartridge was washed with 5 mL of ultrapure water to remove any remaining salt, dried under vacuum. The retained phthalates were then eluted with ethyl acetate (2 × 3 mL) into pre-cleaned vials and the ethyl acetate was completely evaporated under normal atmospheric pressure. Prior to GC–MS analysis, the samples were concentrated with 1 mL ethyl acetate. The final samples were stored in the dark at 4 °C until analysis.

GC–MS analysis

Gas Chromatography Mass Spectrometry (GC MS) Thermo scientific Trace 1310 gas chromatograph coupled to Thermo scientific TSQ 9000 triple quadrupole mass spectrometer manifold (Massachusetts, USA) operated with electron impact ionization was used to determine phthalates’ concentrations. We optimized a method based on EPA method 8270D39. Samples (1 μL) were injected automatically in splitless mode at 280 °C. Chromatographic separation was conducted on a TG5 silica MS column (30 m × 0.25 mm ; 0.25 µm) with the GC oven set to operate at 40 °C for 1 min, 70 °C at 10 °C/min for 2 min, 225 °C at 60 °C/min for 3 min, and 280 °C at 8 °C/min for 4 min. Helium 99.9995% was used as the carrier gas at a flow rate of 1 mL/min. Each sample was measured 3 times, data was collected and analyzed using the Thermo Scientific Xcalibur™ software, Version 4.3 (https://www.thermofisher.com/xcalibur).

Thermogravimetric analysis

TGA was carried out using Shimadzu TGA-50 analyzer (Kyoto, Japan). Phthalate reference compounds were measured under controlled temperature programs that involved heating the samples to 500°C and holding at this temperature for 10 min at different heating rates (10, 15, and 20°C/min). Platinum crucibles were used to carry the phthalates, and the measurements were done at a constant flow rate of N2 as a purging gas (10 mL/min) which was used to avoid the oxidation of the samples.

XRF analysis

The sediment samples were air-dried for 7 days and were subsequently sieved through a 40 mm mesh of prior to X-ray fluorescence spectroscopic determination. XRF analysis was conducted using Thermo Scientific Niton XL3t (Massachusetts, USA) in a total of 3 runs with 90 s for each run.

Quality assurance/quality control performance and data analysis

The spiking method was employed during the quality assurance process to validate the analytical methods. This involved running blank samples alongside each sample set, conducting triplicate analyses of samples, and daily monitoring of conditions by assessing the response factor range of calibration standards and the recovery rates of a test standard included in each run. The maps were created using ArcGIS Maps (Esri, Redlands, CA, USA) embedded in Microsoft Power BI (version 2023)40. The used base-map is the Streets map powered by ESRI. The locations of the collected samples were based on the latitude and longitude taken onsite. On map, the bubble size was proportional to the concentration of the element under investigation.

Statistical analysis

The mean value of the three replicates was calculated for each sample, while standard deviation was used to assess variability and ensure the consistency of the analytical results. This methodology ensures that the findings are statistically significant and reliable for further interpretation and conclusions. Pearson correlation coefficient and principal component analysis (PCA) were employed to uncover associations between contaminants and reduce the dimensionality of the dataset while revealing the underlying pattern. The analysis was conducted using the R programming language41 and the FactoMineR package42. The results of the correlation matrix and PCA were visualized using the corrplot and factoextra R packages43, respectively. The data for DEP and DPB were removed from the dataset due to missing values. The Kaiser–Meyer–Olkin (KMO)44 and Bartlett’s sphericity45 tests were performed to assess whether the observed variables were adequate for PCA.

Results and discussion

Concentrations of toxic metals in seawater and sediments

In this study, we evaluated the levels of contamination in seawater and sediments after collecting samples from 40 sites along the Lebanese Mediterranean coast (Supplementary Fig. 1) with each site reflecting characteristic hotspots (Supplementary Table 1). The average concentrations of the metals in seawater samples along the coastline are reported as follows: 52Cr (8.25–23.87 μg/l), 55Mn (3.04–9.93 μg/l), 56Fe (11.43–78.18 μg/l), 58Ni (3.41–13.58 μg/l), 59Co (0.37–3.97 μg/l), 63Cu (3.12–21.82 μg/l), 64Zn (7.12–13.12 μg/l), 75As (2.98–15.35 μg/l), 80Se (1.12–4.76 μg/l), 98Mo (7.94–33.98 μg/l), 114Cd (0.77–3.08 μg/l), 120Sn (0.68–3.15 μg/l), 202Hg (0.11–2.87 μg/l), and 208Pb (1.14–7.93 μg/l) (Table 1). Upon inspecting the distribution of each metal along the coastline (Fig. 1), we categorized the metals according to low, moderate, and high concentrations based on quantitative concentration thresholds established through preliminary data analysis and relevant environmental standards. Concentrations of Cr, Cu, Mo, Ni, Se, and Sn were highest in the samples gathered from the northern part of the coastline; As, Co, Fe, Mn, Pb, and Zn were highest in the central part of the coastline whereas Cd and Hg were distributed randomly. Next, we classified the distribution of these concentrations in hotspots along the whole coastline such as landfill, resorts, riverbanks, industrial areas or fuel storage facilities, sewage, agricultural lands and coastline cities or environmentally protected areas (Fig. 2). Concentrations of Fe, Mo, Cr and As contributed mostly to landfill garbage; high levels of Fe and Zn were present in samples in the proximity of riverbanks, sewage systems and industrial facilities. Notably, Hg, Sn and Cd levels were not alarming thus indicating that they are within range and do not pose a significant threat to marine life. On the other hand, Mn and Zn levels are acceptable and are both essential trace elements required by many marine organisms for their growth, survival, and reproduction. Next, we examined the distribution of metals in sediments collected along the coastline using XRF spectroscopy. The elements calcium (Ca between 10,000 and 250,000 ppm), iron (Fe between 2000 and 40,000 ppm), strontium (Sr between 50 and 2000 ppm), titanium (Ti between 200 and 1700 ppm), potassium (K between 150 and 800 ppm), selenium (Se between 100 and 900 ppm), barium (Ba between 10 and 1000 ppm), chromium (Cr between 50 and 500 ppm), sulfur (S between 200 and 800 ppm), zirconium (Zr between 20 and 125 ppm), zinc (Zn between 25 and 220 ppm), and manganese (Mn between 50 and 250 ppm) were determined (Fig. 3). Some of these elements were distributed along the whole coast (Ca, Fe, K, Zr, Cr) while others (Sr, Ti, Se, Ba, S, Mn, Zn) had considerable levels only at certain sampling sites. For instance, Sr concentrations were significantly high at locations 6, 34 and 35 where a main city port, an oil refinery and agricultural landscapes are located. Ba was highly present at location 9 which is in proximity of cement industries; and high levels of Zn were detected at location 13 where fuel storage facilities are situated. Our results were supported by studies previously conducted in different regions of the Mediterranean Sea that report average distribution of metals in sediments (Supplementary Table 4). Elevated concentrations of metals like Cr, Cu, Mo, Ni, and Se in the northern region suggest localized contamination sources, while high levels of As, Co, Fe, Mn, Pb, and Zn in the central area are linked to human activities such as agriculture and sewage discharge. The presence of essential trace elements like manganese and zinc is important for marine life, while the risks associated with metals like iron and arsenic from landfill sources highlight the need for pollution mitigation strategies. Sediment analysis further clarified the geochemical complexities and anthropogenic influences on metal distribution. The study emphasizes the necessity for continuous monitoring of metal concentrations and calls for future research to assess their ecological impacts and the effectiveness of pollution control measures.

Table 1 Mean levels of toxic metals and phthalates (in μg/l) present in seawater from 40 sites along the Lebanese coast of the Mediterranean Sea.
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Fig. 1
figure 1

Bubble maps showing the distribution and intensity of toxic metals along the south Mediterranean coast using ArcGIS street maps embedded in Microsoft Power BI (version 2023)40.

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Fig. 2
figure 2

Average concentrations of toxic metals in seawater along the south Mediterranean coast identified by inductively Coupled Plasma Mass Spectrometry (ICP-MS).

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Fig. 3
figure 3

Distribution of metals in sediments collected along the south Mediterranean coast as identified by X-ray Fluorescence (XRF) spectroscopy. The rocky nature of the locations 7, 10, 11, 12, 16, 18, 21, 23, 24, 25, and 32 did not allow collection of sediments.

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Concentrations of phthalates in seawater

Many methods have been widely used for the analysis of phthalates most commonly being the SPE-GC–MS method38. SPE allows for the selective adsorption of phthalates from complex matrices onto a solid phase, followed by their elution with an appropriate solvent. The eluted phthalates are then injected into a GC–MS system for detection and quantification. MS remains one of the most powerful techniques for the identification of unknown compounds using accurate mass measurements46. The GC–MS is sensitive and provides high-resolution separation of the phthalates, which allows for accurate quantification in various matrices47,48. We used 13 phthalate standards (Fig. 4A) to optimize influential factors and efficiency of the SPE extraction procedure including solvent nature, sample volume, and sorbent mass. The gas chromatogram of the phthalate standard mixture exhibited a specific retention time for each phthalate and did not overlap with peaks of other phthalates (Fig. 4B). The retention time and the m/z ratio along with the molecular weight, boiling point, melting point, density, and recovery percentage of the non-deuterated and deuterated phthalates are tabulated in Supplementary Table 5. The difference in the retention time is attributed to the difference in the molecular weight and density. Ethyl acetate showed acceptable recoveries ranging from 75 to 100% while recoveries were less than 50% with n-hexane. Notably, the recovery percentages of phthalates using SPE-GC–MS method are reported to be in the range of 81–99% depending on the matrix and the type of phthalate49. The identification of phthalates extracted from the water samples was then confirmed by GC–MS. The values for the instrument Detection Limit (IDL) were estimated from the linear regression of the standards calibration curves (Supplementary Fig. 3). In addition, we used deuterated phthalates as internal standards to avoid errors from the matrix components originating from differences in the extraction efficiency and the composition between samples and standards. We report the mean concentration levels of the 3 phthalates DEHP (from 15.57 ± 1.3 μg/l to 72.88 ± 1.4 μg/l), DEP (from 10.28 ± 1.3 μg/l to 45.57 ± 1.5 μg/l) and DBP (from 5.62 ± 0.6 μg/l to 16.84 ± 0.7 μg/l) in Table 1. DEHP was the main phthalate in all 40 sampled locations followed by DEP that was present mainly in the middle coast (25 sites) as reported in Fig. 4C, whereas DBP was identified in 9 locations. The high levels of phthalates were recorded in several sites where hotspots included main city ports, sewage discharge, beach resorts, riverbanks, landfills, and industrial areas. The lowest DEHP levels (below 17 μg/l) were in locations 7 and 40 corresponding to resorts and environmentally protected areas, while the highest levels of DEHP were in locations 16 and 24 (above 60 μg/l) corresponding to sewage discharge at coastal cities and main city port. The highest DBP concentration was measured in sewage discharge at a main city port and the highest levels of DEP were mainly detected between sites 17 and 23 close to a city port, power plant, landfills, and industrial areas. The concentrations detected in our study were in the same range reported by Paluselli et al. for the French Mediterranean coast38, by Sanchez-Avila et al. for Spanish coastal water50, and by Neal et al. for the south coast of the UK51. The remaining phthalates were of minor importance with concentrations below 1 μg/l.

Fig. 4
figure 4

(A) The chemical structures of the phthalates and their (B) retention times as identified in the chromatogram from the GC–MS analysis of the mixture of phthalate standards. (C) Histograms showing the percentage concentrations of DEHP, DEP and DBP phthalates at the 40 sampled locations.

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Thermal stability of phthalates

The complex organic load of landfill leachate, sewage discharge and industrial wastewater could all lead to the formation of undesired by-products of phthalates during the oxidation of leachate and may follow several biodegradation pathways52,53. The half-life of the degradation process of phthalates in water usually occurs between 1 day and 2 weeks and is set by different abiotic factors including elevated temperature, increased sunlight, pH, presence of toxic metals and aerobic conditions54. Therefore, the process is predicted to be faster in hotter and sunnier parts of the world, while in cold environments, the degradation half-life may be extended to several years. To get more sights into the stability and degradation process of phthalates, thermogravimetric analysis (TGA) was conducted on the 13 standard phthalates. Figure 5 shows the TGA and differential thermogravimetric (DTG) curves of the investigated phthalates where a zero-order evaporation process was determined by the characteristic sharp peak in the DTG curves. All the phthalates displayed a complete one-step drop in the weight percent in the temperature range (18 – 400 °C) except for DAP which had a first drop of about 80 wt% at 2400C followed by a second drop at 400 °C after losing all the remaining mass. This is attributed to the fact that the DAP and DMP structures share the same core, and the second drop would reflect the loss of the ethylene part present in DAP. Similarly, DTG plot of DBzP exhibited two peaks (300 and 360 °C) and had a final loss of 90% of the initial weight unlike all other phthalates which were completely evaporated by the end of TG measurements. Also, DBzP and DMP structures share the same core, and the second drop would reflect the loss of the benzene rings present in DBzP. Notably, the drop in the weight percent started at higher temperatures for the phthalates with higher boiling points such as DEHP, DPhP, DPEP and DnOP. It is important to mention that TG measurements were performed under different heating rates as shown in Supplementary Fig. 4 for DEP, DBP and DEHP. Upon increasing the heating rate, the temperature at which the phthalates start to lose weight becomes higher thus reflecting a higher activation energy. Notably, hydrolysis is the most common chemical process for the abiotic degradation of phthalate diesters into carboxylic acid and alcohol in municipal landfills. This occurs through two consecutive steps where the monoester and alcohol are first formed then the phthalic acid and a second alcohol result. Facilitated by the presence of toxic metals, the produced phthalic acid then undergoes hydrogenation to form 1,2-cyclohexane dicarboxylic acid. Taken together, the results suggest that phthalates present in wastewater and landfills possess a similar stability where the decomposition of each phthalate depends highly on elevated temperatures. Nevertheless, other environmental effects such as pH levels, salinity, and presence of biodegradable species of phthalates, all affect the decomposition of phthalates55.

Fig. 5
figure 5

TGA and DTG curves of 13 different phthalates at a heating rate of 20 °C/min.

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Statistical analysis of toxic metals and phthalates in seawater

Next, we performed correlation matrix and principal component analysis (PCA) to evaluate the correlation and patterns between the different contaminants. The average distributions of the identified contaminants are illustrated in Supplementary Fig. 5A and Supplementary Table 6. The mean and median values provided insights into the central tendency, while the quartiles delineate the spread of the data. Notably, the metals Cr, Fe, Ni, Cu, Mo, and the phthalate DEHP exhibited a relatively wide concentration ranges, suggesting potential variability in their sources or environmental conditions. Cr ranges from 8.25 to 30.34 μg/l (mean 15.78) and shows 3 outliers, Fe ranges from 11.43 to 78.18 μg/l (mean 28.24), Ni ranges from 3.41 to 13.58 μg/l (mean 6.899) and shows one outlier. Cd and Pb concentrations are with typical ranges for environmental analysis (Cd from 0.77 to 3.48 with a mean of 1.72, Pb from 1.14 to 7.93 with a mean of 3.79). We performed further correlation statistical analysis to explore relationships between the variables. We first computed the pairwise correlation between all the components based on their Pearson correlation coefficients. We defined next a function to conduct the pairwise correlation tests between the different features in the dataset and returns p-values correlation matrix. The heatmap plot represents the visualization of the computed correlation coefficients with three different significance levels (Fig. 6). Cr shows positive correlations with Ni (0.64), Cu (0.55), Co (0.5), Hg (0.32) and Se (0.59) while a negative correlation with As (- 0.38) occurs. Mn has positive correlations with Fe (0.38), Zn (0.43), Sn (0.39), Hg (0.44), Pb (0.33), and Cd (0.52). Fe correlates positively with Cd (0.47), Co (0.34), Cu (0.34), Zn (0.37), Sn (0.38) and DEHP (0.41). Ni exhibits positive correlations with Cr (0.64), Cu (0.52), Se (0.55) and negative correlation with Zn (- 0.27). Pb shows positive correlations with Co (0.75), Cu (0.44) and Zn (0.52) while Cd correlates positively with Ni (0.38), Cu (0.47) and Sn (0.53). Equally important, DEHP displays positive correlations with Fe (0.41), Co (0.54), Zn (0.34), As (0.46), Sn (0.54), Hg (0.35), and Pb (0.49). Positive correlations indicate that as the concentration of one element increases, the concentration of the correlated element tends to increase as well. Conversely, negative correlations suggest an inverse relationship, whereby an increase in one element is associated with a decrease in the correlated element. To assess whether the observed variables are adequate for PCA, we performed the Kaiser–Meyer–Olkin (KMO) and Bartlett’s sphericity tests with outcome results of 0.74 and 1069 (p-value < 0.05), respectively. This confirmed that PCA is suitable for applying the approach of reducing dimensionality. PCA was then carried out to extract the important information from the dataset and express this as a set of a few new variables called principal components, along which the variation in the data is maximal. In PCA, eigenvalues and their associated variance percentages are crucial for understanding the contribution of each principal component to the overall variability in the dataset. Accordingly, the visualization of PCA throughout the Scree plot assesses the relationship between the different contaminants and sampling sites The scree plot underscored the percentage of explained variation by each component, which was then emphasized by the cumulative relative variation plot of the first 10 components (Supplementary Fig. 5B-C). According to the results, the first component explains more than 50% of the variation in the data, the second component describing approximately 24% of the variation, with the first 4 components justifying up to 90% of the variability. The variables correlation plot (Fig. 6) illustrates how well different variables are represented on the first two principal components and their associations among all variables. Variables that exhibit positive correlations are clustered together, while those with negative correlations are positioned in opposite quadrants relative to the plot origin. The distance of variables from the origin serves as a measure of their quality on the factor map, with greater distances indicating more accurate representation. The color coding corresponds to the variation of cos2 values, which reflects the quality of the representation. High cos2 values, seen as variables positioned near the circumference of the correlation circle, denote that the principal components are strongly represented. Contrarywise, lower cos2 values suggest less precise representation by the principal components. Supplementary Fig. 5D-F represents the relative contributions plot of the variables to the overall variability of the principal components. The variables that correlate with PC1 and PC2 are paramount for explaining the variance within the dataset. The bar plots illustrate the top 10 variables influencing the dimensions 1 and 2 compared to the anticipated average contribution of 6.7% based on the 15 variables in the dataset. PC1 displays strong positive correlations with As (0.95), Zn (0.91), Pb (0.85), Co (0.84), DEHP (0.76) while being negatively correlated with Cu (- 0.61), Mo (- 0.71), Cr (- 0.94), Ni (- 0.95), Se (- 0.96). Equally important, PC2 displays strong positive correlations with Sn (0.93), Hg (0.78), Cd (0.75), Mo (0.67), Cu (0.58) and contributes significantly to the variation by PC2. The strong correlations suggest that PC1 and PC2 capture significant variation in the dataset related to these variables and thus a potential association with specific environmental sources or pollution influences. Correlation analysis in environmental studies helps identify relationships between elements, indicating common sources, pathways, or processes. Positive correlations suggest that elements increase together, often pointing to shared pollution sources, while negative correlations highlight opposing behaviors. These insights aid in distinguishing natural from anthropogenic contributions, predicting contamination patterns, and assessing ecological risks. Understanding these interactions allows for targeted remediation strategies and improves monitoring efforts by providing a holistic view of pollutant dynamics. The positive correlations reflect the fact that these emerging contaminants are most likely originating from polluting sources such as industrial activities, atmospheric deposition landfill waste, while negative correlations potentially indicate common geological or anthropogenic sources56.

Fig. 6
figure 6

Correlation matrix and Principal component analysis (PCA) of the contaminants. (A) The heatmap plot represents the visualization of the correlation matrix with three different significance levels (0.001, 0.01, 0.05 marked by ***, **, and * respectively). Insignificant correlations are left blank in the lower part of the plot. Note that DEP and DPB were removed from the correlation analysis since both contaminants were not detected in many sampling sites. (B) The correlation plot of variables illustrates the degree to which different variables are represented on the first two principal components and their interrelationships. Positively correlated variables are clustered together, while negatively correlated variables are positioned in opposite quadrants of the plot origin. The distance of variables from the origin reflects their quality on the factor map, with those farther away being more accurately depicted. Variables are color-coded based on their cos2 values, indicating the quality of their representation. A high cos2 value suggests a strong representation of the variable on the principal component, with the variable positioned close to the circumference of the correlation circle. Conversely, a low cos2 value indicates that the variable is not well represented by the principal components.

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Overall, the analysis identified a broad spectrum of metals in seawater samples, utilizing microwave-assisted digestion and ICP-MS for precise measurement. The observed concentration ranges for various metals (e.g., Cr: 8.25–23.87 mg/l, Fe: 11.43–78.18 mg/l, As: 2.98–15.35 mg/l) indicate a pronounced variability across sampling locations. This variability was notably influenced by localized hotspots, with specific metals like Cr, Cu, Mo, Ni, Se, and Sn concentrated in the northern coastline, while As, Co, Fe, Mn, Pb, and Zn peaked in central areas. The random distribution of Cd and Hg suggests that these metals may be influenced by diverse sources or sporadic contamination events. The elevated levels of certain metals, particularly in proximity to landfills, industrial facilities, and sewage systems, underscore the potential anthropogenic influences on marine ecosystems. Notably, while Mn and Zn were present in acceptable levels—indicating their essential roles for marine organisms—high concentrations of other metals such as Cr and Cu warrant concern due to their potential toxicity. XRF spectroscopy revealed a detailed elemental composition of sediments, highlighting significant concentrations of Ca, Fe, Sr, Ti, K, and others. The pronounced presence of Sr near city ports and oil refineries, and the elevated levels of Ba near cement industries, indicate localized sources of contamination. These findings reflect the impacts of industrial activities and urban runoff on sediment quality, which can have long-term implications for benthic organisms and overall coastal health. Additionally, our study successfully employed SPE-GC–MS to analyze phthalate levels, revealing DEHP as the most abundant compound across all sites, with concentrations peaking at sewage discharge points and city ports. This finding aligns with other Mediterranean studies, confirming widespread contamination. The consistent recovery rates from the extraction process suggest a robust methodology, allowing for reliable quantification of these persistent pollutants. The presence of phthalates in high concentrations near urban and industrial areas poses risks to marine biodiversity, as these compounds are known to disrupt endocrine systems and affect reproductive health in aquatic organisms. Notably, the thermogravimetric analysis demonstrated that phthalates degrade at varying rates under different environmental conditions, primarily influenced by temperature and exposure to light. This highlights the importance of abiotic factors in the degradation processes, which can vary widely across the Lebanese coastline due to its diverse climate and anthropogenic activities. To strengthen the understanding of the outcomes of our study, the correlation matrix and PCA provided valuable insights into the relationships between toxic metals and phthalates. The strong positive correlations among metals like Cr, Ni, Cu, and As, along with DEHP, suggest potential shared sources of contaminants, likely linked to industrial activities and urban runoff. Conversely, the negative correlations observed indicate the complexity of interactions among contaminants, revealing the intricate balance of marine ecosystems.

Metals are often categorized as light, heavy, and metalloids; toxic, or traces based on chemical and physical properties such as density, atomic weight, atomic number, and degree of toxicity57. Certain metals are required for plant development as well as animal and human health. Nevertheless, at high doses, they become poisonous and xenobiotic. As per the World Health Organization (WHO), the prevalent toxic metals of public health concerns comprise beryllium (Be), aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), molybdenum (Mo), silver (Ag), cadmium (Cd), tin (Sn), antimony (Sb), barium (Ba), mercury (Hg), thallium (Tl) and lead (Pb)58,59,60,61. The major source of Fe, Cd, Ni, Pb and Se in the environment is weathering of rocks and soils, however anthropogenic sources such as emissions from burning fossil fuels also contribute to natural waters. Additionally, a major source of these metals in seawater originates from direct industrial waste effluents into the sea and usage of metal-containing phosphate fertilizers. Metals are categorized into two groups according to their source: natural or anthropogenic. Natural sources encompass terrestrial and marine volcanic eruptions, surface winds, forest fires, erosion, biogenic, meteoric, and rock weathering. Anthropogenic sources, such as agricultural runoff, mining, paints, treated timber, lead-acid batteries, high traffic loads, industrial wastes, occupational exposure, and microplastics floating in the oceans, contribute to the release of pollutants into various environmental bodies. Industries correspond to the most significant anthropogenic source of toxic metal pollution due to contaminated air emissions and waste disposal. Many of these metals can be found in the aquatic environment in cationic forms (Cd2+, Zn2+, Cr3+, Hg2+, and Pb2+), oxyanions (AsO43-, SeO42-, and CrO42-), or organic forms ((CH3)2Hg).

For instance, Ni, As and Cd infiltrate the environment through volcanic activity, metal-ore processing, and forest fires. Ni–Cd-loaded batteries, phosphate fertilizers, detergents, refined petroleum products, cosmetic industries, and photoelectric cells are all anthropogenic sources. Ni, As and Cd poisoning cause renal failure, bone deterioration, gastrointestinal distress, liver and nervous system damage as well as cancer2,62. Although Cr is found naturally in rocks and soils, electroplating, combustion of fossil fuels, and plastic manufacturing, add to its anthropogenic sources where heavy dosages induce gastrointestinal discomfort, stomach ulcers, renal and liver damage. Notably, Cu is a trace metal essential for biological systems facilitating enzyme activation during photosynthesis; but in larger amounts Cu dust exposure produces nose, eye, and mouth irritation, nausea, diarrhea, kidney damage, anemia, and gastrointestinal diseases. Equally important, Pb occurs naturally in the earth’s crust and is extensively used in pipes, batteries, bullets, cable coverings, and radiation shielding sheets. Pb is hazardous to the kidneys, the nervous and reproductive systems and causes irreparable brain damage as well as fecal development, delayed growth and learning disabilities. Hg naturally occurs in the soil due to weathering of rocks and volcanic eruptions. Anthropogenic Hg, on the other hand, originates from the metal’s extensive use in industries, such as mining, batteries, Hg vapor lamps, electronic industries, plastics and pharmaceuticals. Hg exposure results in mental disorders and physical deformities. Zn is also an essential nutrient in human diet, but high levels of Zn poisoning induce anemia, pancreatic damage, and cholesterol issues.

Equally important, the toxicity of phthalates remains a subject of debate, marked by the conflict between their commercial significance and their potential impact on human health and the environment. Phthalates, which are plasticizers not chemically bonded to products, are readily released into the environment from various sources, including municipal wastewater, sewage sludge, industrial solid waste, leaching, migration, among others63,64. Despite being non-persistent and capable of biodegradation in the environment, phthalates are extensively present in water bodies due to the continuous dispersion and the widespread use of plastics. DMP is used in plastics, safety glasses, rubber coating agents, molding powders, insect repellants, and pesticides65. Acute short-term exposure to DMP results in irritation of the eyes, nose, and throat. Animal studies reported effects on growth and on the kidney from chronic oral exposure66. DEP is used in manufacturing plastics, insecticides, cosmetics, and aspirin, and is found in toothbrushes, automobile parts, toys, tools, and food packaging67. Contact with DEP can irritate the skin and eyes while longer exposure causes headache, dizziness, nausea, and damage in the nervous system. DAP self-polymerizes and is mainly used for low-pressure laminated cloth and paper. This compound is toxic by ingestion, causes irritation of the eyes, and is absorbed by the skin and mucous membranes68. DiBP, DHxP and DBP are widely used in floorings, adhesives, lacquers, inks, hydraulic fluids, and lubricants despite being identified as male/female reproductive toxicants and responsible of birth defects69,70. DEHP is the most common plasticizer used in medical devices such as nasogastric tubes, dialysis bags, blood bags, transfusion, and air tubes. Acute exposure to large oral doses of DEHP can cause gastrointestinal distress, and developmental failure and is classified by EPA as human carcinogen71.

One major ecological concern is the contamination of sea water by phthalates that enter the marine environment directly through the disposal of plastic waste72 or the discharge of sewage and runoff of agricultural areas73. In addition, phthalates can be released into the air and deposited into the ocean through atmospheric processes74. Once in the marine environment, phthalates accumulate in sediments and biota, and can be transported through ocean currents, leading to their widespread distribution75. Indeed, the long-range transport of phthalates has been documented through measurements in remote areas, such as the Arctic, where they have been found at elevated concentrations76. Besides water, phthalates can accumulate in the tissues of marine organisms, including fish, shells, and mammals. This raised concerns about the potential impacts on the health of these organisms and the safety of seafood for human consumption. A study by Wang et al. found that phthalates were present in the muscle tissue of fish collected in the mangrove wetland in Dongzhai Harbor, China77. Similar findings were reported by Vethaak et al. in a study of the Eastern Scheldt and the North Sea near Noordwijk, Netherlands78. The accumulation of phthalates was also present in other tissues of marine organisms, including shrimp79, mussels80, and dolphins81. Under all these circumstances, phthalates were placed in the list of priority pollutants abided by the USA Environmental Protection Agency (USEPA), the European Union, and Chinese waters82,83. Phthalates can biomagnify in marine food chains, with potentially negative impacts on the safety of seafood for human consumption. A study by Kuang et al. found that exposure to phthalates was associated with reduced growth and reproduction in the marine alga Scenedesmus obliquus84. Similarly, a study by Orbea et al. reported the association of phthalates with oxidative stress and DNA damage in the mussel Mytilus galloprovincialis85. Other studies also reported reduced survival and growth in fish86, impaired fertilization success in mussels87, and immune system suppression in shrimps88. Most importantly, the consumption of seafood contaminated with phthalates was linked with an increased risk of preterm birth in pregnant women89 and allergic diseases in children90.

Conclusion

Wastewater has a detrimental effect on humans in terms of health, social, economic, and cultural aspects. Since 2004, the World Health Organization (WHO) has advocated for the implementation of the Water Safety Plan (WSP) as a measure to mitigate wastewater contamination in waterbodies. Thus, conducting water-related research and its contaminating agents are necessary measures to protect water resources. In this study, water samples from 40 locations along the Lebanese coast were examined for the presence of phthalates. Using GC–MS, the phthalates were detected, and the results show that they are distributed along the coast with DEHP emerging as the predominant species. We highlight significant contamination along the Lebanese Mediterranean coast, with toxic metals and phthalates originating primarily from domestic and industrial activities. Elevated levels of metals like Cr, Fe, and As indicate anthropogenic pollution, while low Hg, Sn, and Cd levels suggest limited immediate ecological risk. The widespread presence of DEHP as the dominant phthalate underlines the risks posed to marine ecosystems and human health. Addressing these challenges requires urgent improvements in wastewater treatment infrastructure, stricter regulations on industrial discharge, and adherence to international environmental standards to protect coastal waters and aquatic life. This research provides valuable insights into specific contaminants, setting a strong foundation for future studies to build upon. Expanding the scope of contaminants, implementing long-term monitoring programs, and conducting broader regional studies will enhance understanding of trends, spatial variations, and mitigation strategies. Collaborative efforts focusing on bioaccumulation, climate change, and cross-regional comparisons will further support the development of effective policies and the preservation of marine ecosystems.