Table 1 Treatment effects on beta diversity.

Metal	Dose	Exposed vs Sham Control			Dose Effect		Pre- vs Post-Exposure
Metal	Dose	Equal Variance^a	Effect Size^b	P ^c	Effect Size^b	P ^c	Equal Variance^a	Effect Size^b	P ^c
Arsenic	Control	NA			NA		0.414	0.087	0.750
	Low	0.957	0.376	0.008	0.133	0.002	0.295	0.458	0.008
	Mid	0.001	0.268	0.007	0.066	0.045	0.236	0.257	0.009
	High	0.187	0.443	0.006	0.192	0.001	0.262	0.454	0.006
Cadmium	Control	NA			NA		0.258	0.115	0.417
	Low	0.602	0.245	0.016	0.111	0.004	0.989	0.193	0.061
	Mid	0.237	0.352	0.007	0.117	0.003	0.478	0.264	0.014
	High	0.684	0.373	0.009	0.143	0.003	0.559	0.393	0.007
Cobalt	Control	NA			NA		0.798	0.083	0.736
	Low	0.947	0.070	0.905	0.029	0.957	0.668	0.082	0.796
	Mid	0.709	0.157	0.128	0.088	0.062	0.576	0.146	0.166
	High	0.281	0.172	0.093	0.084	0.103	0.098	0.212	0.015
Chromium	Control	NA			NA		0.417	0.182	0.135
	Low	0.393	0.155	0.147	0.064	0.188	0.9	0.203	0.050
	Mid	0.853	0.158	0.137	0.077	0.068	0.261	0.151	0.145
	High	0.937	0.215	0.007	0.100	0.023	0.423	0.204	0.008
Nickel	Control	NA			NA		0.213	0.146	0.390
	Low	0.110	0.533	0.007	0.244	0.001	0.023	0.594	0.007
	Mid	0.456	0.457	0.008	0.139	0.004	0.001	0.539	0.009
	High	0.446	0.553	0.008	0.138	0.007	0.602	0.629	0.007

Results from the PERMANOVA test on each cohort, comparing post-exposure control samples to post-exposure treated samples (“Exposed vs Sham Control”). Dose-dependent effects are shown under “Dose Effects.” PERMANOVA tests comparing pre and post-exposure samples are shown under “Pre- vs Post-Exposure.” ^aResults of a multivariate test of equality of variances using the “Betadisper” function from the vegan R package. Statistical significance indicates that the variances are not equal. ^bThe proportion of variance explained by exposure status. ^cThe probability that both sample groups occupy the same location (have similar microbiome compositions) based on the Bray-Curtis distance metric using the PERMANOVA test. P values less than 0.05 are in bold.

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