http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/Wat%20Res13,%20241.pdf

Sorption of hydrophobic pollutants on natural sediments

Because it is very toxic and accumulates in organisms, particularly in fish, mercury is an important pollutant and one of the most studied. Nonetheless we still have an incomplete understanding of the factors that control the bioconcentration of mercury. Elemental mercury is efficiently transported as a gas around the globe, and even remote areas show evidence of mercury pollution originating from industrial sources such as power plants. Besides elemental mercury, the major forms of mercury in water are ionic mercury (which is bound to chloride, sulfide, or organic acids) and organic mercury, particularly methylmercury. Methylmercury rather than inorganic mercury is bioconcentrated because it is better retained by organisms at various levels in the food chain. The key factor determining the concentration of mercury in the biota is the methylmercury concentration in water, which is controlled by the relative efficiency of the methylation and demethylation processes. Anoxic waters and sediments are an important source of methylmercury, apparently as the result of the methylating activity of sulfatereducing bacteria. In surface waters, methylmercury may originate from anoxic

/pdf/the-chemical-cycle-and-bioaccumulation-of-mercury-53npodz0gl.pdf

The chemical cycle and bioaccumulation of mercury

Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.

Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation

Semi-empirical estimation of sorption of hydrophobic pollutants on natural sediments and soils

A principal goal of pesticide science is to be able to predict the environmental impact of a pesticide before it is released into the environment. To save expense and time, we would like to be able to make such a prediction for each pesticide with as few laboratory experiments on the pesticide as possible, and even fewer field experiments. Environmental processes, however, are enormously complex and sometimes (apparently) random. The sites of most interest—agricultural fields, forests, lakes, streams, etc.—are subtle living ecosystems which are incompletely understood and subject to great variability in space and time. The very diversity and intricacy which are indicators of the health of such ecosystems makes even the definition of what constitutes a significant impact on such systems a difficult task.

The SCS/ARS/CES pesticide properties database for environmental decision-making.

Kinetics of chemical degradation of malathion in water

Dynamics of 2,4-D esters in surface waters. Hydrolysis, photolysis, and vaporization

Light-induced transformations of methoxychlor in aquatic systems

Previous studies have focused on N-nitroso derivatives of relatively non-persistent pesticides or pesticides that form unstable N-nitroso derivatives. We feel that more persistent pesticides or their degradative products capable of forming N-nitroso derivatives should be investigated. Also pathways of degradation, both chemical and biological, should be elucidated.

N-nitrosamine formation from atrazine.

Lack of data on the fate and impact of pesticides in freshwater systems prompted Environmental Protection Agency researchers in 1971 to select 10 representative materials (Figure 1) for detailed study. One of the needs highlighted
at that time was for more reliable data on the rates, routes, and products of transformation. Subsequently, Paris and Lewis1 comprehensively reviewed the literature on microbial, chemical, and photochemical transformations of these materials and have since completed microbial studies with them.

John A. Gordon

Papers

Kinetics of chemical degradation of malathion in water

Dynamics of 2,4-D esters in surface waters. Hydrolysis, photolysis, and vaporization

Light-induced transformations of methoxychlor in aquatic systems

N-nitrosamine formation from atrazine.

Chemical and Photochemical Transformation of Selected Pesticides in Aquatic Systems