Impact of dissolved organic matter and environmental factors on methylmercury concentrations across aquatic ecosystems inferred from a global dataset

Mercury (Hg) input into ecosystems is estimated to have increased by twofold to fivefold since the industrial revolution. In aquatic ecosystems, methylmercury (MeHg) receives the most attentions of all the Hg species due to its neurotoxicity and strong bioaccumulation capacity in food chain. Dissolved organic matter (DOM) is crucial in impacting aquatic Hg transformation. However, only few spatially constrained studies have attempted to quantify the relative importance of DOM and other factors (e.g., Hg availability, temperature, pH, and land-use type) on MeHg concentration. In this study, we collected data of 585 water samples at 373 sites globally, including lakes, rivers, estuaries, and wetlands, and characterized the global pattern of MeHg distribution and environmental drivers of aquatic MeHg concentration. Our results showed that MeHg concentrations ranged from detection limits to 11 (geometric mean 0.11 and average 0.29) ng/L, and the highest MeHg concentration and Hg methylation potential were observed in wetlands. A positive relationship was observed between MeHg fraction in the total mercury (THg) and DOM for all the aquatic ecosystems. Using the structural equation modeling, we found that Hg availability was a dominant factor in impacting water MeHg concentration followed by DOM. According to 129 samples of specific DOM source information, we found that the percentage of THg as MeHg (%MeHg) in water dominated by the autochthonous DOM was higher than that dominated by the allochthonous DOM. Our results could advance understanding of aquatic Hg cycling and their environmental drivers, which are fundamental for predicting and mitigating MeHg productions and its potential health risks for humans.

Studying the influence of seasonal conditions and period of exposure on trace element concentrations in the moss-transplant Pylaisia polyantha

This study evaluates the effects of seasonal conditions and exposure periods on trace element concentrations in samples of the epiphytic moss Pylaisia ​​polyantha when transplanted into urban areas. This assessment was carried out in summer and winter at four sites differing in their level of technogenic trace element load. The contents of 25 trace elements (As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, La, Lu, Mo, Nd, Rb, Sb, Sc, Sm, Sr, Tb, Th, U, Yb, and Zn) were determined using neutron-activation analysis, and it was shown that seasonal conditions do not affect vital activity in P. ​​polyantha graft moss. For most elements, the greatest increase in trace element concentration in P. ​​polyantha transplant moss was observed within one month. The high sensitivity of this epiphytic moss-transplant to the level of technogenic load has thus been demonstrated, and it may find utility in future research with similar objectives.