Environmental processes controlling the fate and transport of aristolochic acid in agricultural soil and copper in contaminated lake sediment

Summary

Fate and transport of toxic chemicals are important processes that describe how chemicals move and transform in the environment. Environmental processes such as adsorption, solubility, complexation, dissolution/precipitation, oxidation/reduction, plant uptake and biodegradation play major roles in controlling the fate and transport of chemicals. Understanding these processes is essential to assess the potential of human health risks, the exposure pathway or even the methods for prevention and... Show moreFate and transport of toxic chemicals are important processes that describe how chemicals move and transform in the environment. Environmental processes such as adsorption, solubility, complexation, dissolution/precipitation, oxidation/reduction, plant uptake and biodegradation play major roles in controlling the fate and transport of chemicals. Understanding these processes is essential to assess the potential of human health risks, the exposure pathway or even the methods for prevention and remediation of these risks. Environmental problems can be caused by organic or inorganic chemicals and they have different fate and transport behavior in the environment. In this study, the fate and transport of Aristolochic acids (AAs) in soil and copper in sediment were used as examples to show the different behavior of organic and inorganic chemicals that induced problems in environment.AAs were believed to be causal agents that induced Balkan Endemic Nephropathy (BEN) by food contamination. They are active chemicals in Aristolochia species plants which are extensively found in the endemic villages. This study examined the essential environmental partitioning processes that control fate and transport of AAs. The results showed that the octanol-water partitioning coefficient (Kow) of AAs decreased when pH increased, which indicated the different hydrophobicity between neutral and anion forms. This trend was similar to the soil -water partitioning coefficient (Kd). Solubility (Sw) increased when pH increased. These suggested that AAs will be highly mobile in an alkaline environment. The Kow and Sw were increased when a calcium ion presented in solution. Even if AAs had a high sorption capacity to the soils, they had a high tendency to be desorbed too. The soil adsorption and desorption experiment indicated the cation bridging mechanism may play a major role in soil processes. Root exudates are not the main pathway that release AAs to the soil, but their seed decomposition can release a large amount of AAs, which can be degraded by microorganisms. The plant uptake showed AAs had high accumulation in the roots but less translocation to shoots. All evidence suggested the food contamination hypothesis is possible.Torch Lake, Houghton County, Michigan, which was impacted by copper mining waste, showed a persistent high level of copper in the top sediment. This copper can never be remediated by natural processes. I hypothesized that copper was released from mining waste by microbial mediate reactions and was sequestrated by organic matter and bacteria in the post sediment. To test this hypothesis, the fate and transport of copper were studied with the Phreeqc computer modelwhere the biogeochemical processes (e.g. complexation, precipitation, adsorption, reductive dissolution and biodegradation) were applied to the diffusion process. The results showed that oxidation/reduction conditions highly impact copper fate and transport in sediment. The TEAP process causes the sediment to enter the reducing condition and dissolve the copper waste to pore water. The bacteria in the top sediment adsorbed a large amount of copper but this sorption turned to more stable minerals as time proceeded. Due to the removal of copper by precipitation process, the copper which contributed the solid phases in the top sediment were expected from overlay water. This study showed that this modeling approach is an effective tool to describe the persistent high concentration of copper inTorch Lake sediment. Show less