Forest fires, coal use, and other activities emit mercury. Wetland microbes turn it into a neurotoxin. In freshwater wetlands of the Great Lakes region, a team showed the influence of wetland vegetation in regulating mercury toxicity. They also showed that enhanced production of toxic mercury in certain vegetated areas is associated with three factors: (1) degradation of dissolved organic matter, which comes from decomposing plants and other sources, (2) a shift in the microbial community toward fermentative microbes (like those used in bread making), and (3) changes in the microbiome structure toward Clostridia species.