Investigation of biogeochemical controls on the formation, uptake and accumulation of methylmercury in rice paddies in the vicinity of a coal-fired power plant and a municipal solid waste incinerator in Taiwan
Journal
Chemosphere
Journal Volume
154
Pages
375-384
Date Issued
2016
Author(s)
Abstract
Recent studies have shown that rice consumption is another critical route of human exposure to methylmercury (MeHg), the most toxic and accumulative form of mercury (Hg) in the food web. Yet, the mechanisms that underlie the production and accumulation of MeHg in the paddy ecosystem are still poorly understood. In 2013 and 2014, we conducted field campaigns and laboratory experiments over a rice growing season to examine Hg and MeHg cycling, as well as associated biogeochemistry in a suite of paddies close to a municipal solid waste incinerator and a coal-fired power plant station in Taiwan. Concentrations of total Hg and MeHg in paddy soil and rice grain at both sites were low and found not to exceed the control standards for farmland soil and edible rice in Taiwan. However, seasonal variations of MeHg concentrations observed in pore water samples indicate that the in situ bioavailability of inorganic Hg and activity of Hg-methylating microbes in the rhizosphere increased from the early-season and peaked at the mid-season, presumably due to the anoxia created under flooded conditions and root exudation of organic compounds. The presence of Hg-methylators was also confirmed by the hgcA gene detected in all root soil samples. Subsequent methylation tests performed by incubating the root soil with inorganic Hg and an inhibitor or stimulant specific for certain microbes further revealed that sulfate-reducers might have been the principal Hg-methylting guild at the study sites. Interestingly, results of hydroponic experiments conducted by cultivating rice in a defined nutrient solution amended with fixed MeHg and varying levels of MeHg-binding ligands suggested that chemical speciation in soil pore water may play a key role in controlling MeHg accumulation in rice, and both passive and active transport pathways seem to take place in the uptake of MeHg in rice roots. © 2016 Elsevier Ltd.
Subjects
Biogeochemistry; Methylmercury; Paddy soil; Rice; Root uptake
Other Subjects
Alkylation; Bacteria; Biogeochemistry; Chemical contamination; Chemical speciation; Coal; Coal fueled furnaces; Cultivation; Fossil fuel power plants; Mercury (metal); Mercury compounds; Municipal solid waste; Power plant laboratories; Refuse incinerators; Soil testing; Soils; Sulfur compounds; Waste incineration; Water; Biogeochemical controls; Coal-fired power plant; Methyl mercury; Municipal solid waste incinerator; Paddy soils; Rice; Root uptake; Uptake and accumulations; Soil pollution; coal; mercury; methylmercury; water; coal; mercury; methylmercury derivative; soil; soil pollutant; solid waste; agricultural soil; bioaccumulation; biogeochemistry; biological uptake; coal-fired power plant; mercury (element); methylmercury; municipal solid waste; organic pollutant; paddy field; porewater; rice; root; seasonal variation; soil pollution; soil water; active transport; agricultural land; Article; bioavailability; biogeochemistry; electric power plant; grain; growing season; methylation; microorganism; municipal solid waste; nonhuman; nutrient solution; passive transport; plant root; prevalence; rhizosphere; rice; seasonal variation; soil; sulfate reducer; Taiwan; analysis; chemistry; electric power plant; environmental monitoring; food chain; food contamination; human; incineration; metabolism; microbiology; Oryza; soil pollutant; solid waste; waste management; Taiwan; Biological Availability; Coal; Environmental Monitoring; Food Chain; Food Contamination; Humans; Incineration; Mercury; Methylmercury Compounds; Oryza; Plant Roots; Power Plants; Rhizosphere; Soil; Soil Microbiology; Soil Pollutants; Solid Waste; Taiwan; Waste Management; Water
Type
journal article