U.S. Environmental Protection Agency, Region-10, Seattle, WA, USA.
U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH, USA.
Environ Pollut. 2021 Feb 15;271:116369. doi: 10.1016/j.envpol.2020.116369. Epub 2020 Dec 22.
Thousands of abandoned mines throughout the western region of North America contain elevated total-mercury (THg) concentrations. Mercury is mobilized from these sites primarily due to erosion of particulate-bound Hg (THg-P). Organic matter-based soil amendments can promote vegetation growth on mine tailings, reducing erosion and subsequent loading of THg-P into downstream waterbodies. However, the introduction of a labile carbon source may stimulate microbial activity that can produce methylmercury (MeHg)-the more toxic and bioaccumulative form of Hg. Our objectives were to investigate how additions of different organic matter substrates impact Hg mobilization and methylation using a combination of field observations and controlled experiments. Field measurements of water, sediment, and porewater were collected downstream of the site and multi-year monitoring (and load calculations) were conducted at a downstream gaging station. MeHg production was assessed using stable isotope methylation assays and mesocosm experiments that were conducted using different types of organic carbon soil amendments mixed with materials from the mine site. The results showed that >80% of the THg mobilized from the mine was bound to particles and that >90% of the annual Hg loading occurred during the period of elevated discharge during spring snowmelt. Methylation rates varied between different types of soil amendments and were correlated with the components of excitation emission matrices (EEMs) associated with humic acid fractions of organic matter. The mesocosm experiments showed that under anoxic conditions carbon amendments to tailings could significantly increase porewater MeHg concentrations (up to 13 ± 3 ng/L). In addition, the carbon amendments significantly increased THg partitioning into porewater. Overall, these results indicate that soil amendment applications to reduce surface erosion at abandoned mine sites could be effective at reducing particulate Hg mobilization to downstream waterbodies; however, some types of carbon amendments can significantly increase Hg methylation as well as increase the mobilization of dissolved THg from the site.
数千个废弃矿场遍布北美西部地区，这些矿场中含有大量的总汞（THg）。汞从这些地点释放出来，主要是由于颗粒结合态汞（THg-P）的侵蚀。基于有机物的土壤改良剂可以促进尾矿上的植被生长，减少侵蚀和随后将 THg-P 加载到下游水体中。然而，引入易降解的碳源可能会刺激微生物活性，从而产生甲基汞（MeHg）——汞的毒性和生物累积性更强的形式。我们的目标是通过野外观察和控制实验相结合，研究不同有机物基质的添加如何影响汞的释放和甲基化。在该地点下游采集水、沉积物和孔隙水的现场测量，并在下游测站进行多年监测（和负荷计算）。使用稳定同位素甲基化测定和使用不同类型的有机碳土壤改良剂与来自矿场的材料混合的中尺度实验来评估 MeHg 的产生。结果表明，从矿场释放的 THg 中有>80%与颗粒结合，>90%的汞负荷发生在春季融雪期间排放增加的时期。甲基化率因不同类型的土壤改良剂而异，与与有机物腐殖酸部分相关的激发发射矩阵（EEMs）的成分有关。中尺度实验表明，在缺氧条件下，尾矿中的碳改良剂可显著增加孔隙水中的 MeHg 浓度（高达 13±3ng/L）。此外，碳改良剂显著增加了 THg 向孔隙水的分配。总的来说，这些结果表明，在废弃矿山场地应用土壤改良剂来减少表面侵蚀，可以有效减少颗粒态汞向下游水体的释放；然而，某些类型的碳改良剂可以显著增加汞的甲基化，以及从场地释放溶解态 THg。
