Aquatic ecosystem pesticide accumulation

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) ai e toxic compounds of anthropogenous origin, able to accumulate in tissues of alive organisms and to cause different diseases. These compounds ai e the most dangerous for aquatic ecosystems as they easily adsorb in sludge and ai e included in food chains of biota. Humans consume PCBs and OCPs mostly with fish. 

Model ecosystems have been used for about 8 years to measure the distribution and fate of pesticides in the aquatic environment. Over that period of time numerous design changes have evolved that have increased the versatility of the ecosystem and improved simulation of environmental conditions. In our laboratory, we have used the static model ecosystem primarily to model the pond or small lake environment, and to simulate the likely rates and modes of pesticide entry (1). More recently, we have developed larger systems capable of providing sufficient biomass for accumulation and dissipation rate determinations (2) and for metabolic studies (3). 

Environmental residues of pyrethroids and pyrethr-ins are degraded by hydrolysis, and pyrethrins by photolysis, and so do not accumulate in most ecosystems. The main environmental hazard associated with pyrethroid use is contamination of freshwater by acute run-off after use as an agricultural pesticide or ectoparisitide near to water, which can lead to death of aquatic invertebrates or fish (which have very limited pyrethroid detoxification capacity). 

Carbary I (1-naphthyl methylcarbamate) is a chemical in the carbamate family used chiefly as an insecticide. It is a colorless white crystalline solid. Carbaryl disrupts the nervous system by adding a carbamyl moiety to the active site of the acetylcholinesterase enzyme, which prevents it from interacting with acetylcholine.1 It is classified as a likely human carcinogen by the EPA. The pesticide is used indiscriminately, so the toxicity has raised public concern about the ecosystem and human health. Carbaryl is lethal to many non-target insects such as the honeybee. Accumulation of the pesticide occurs in many aquatic organisms such as catfish and algae.2 Due to public health and ecosystem concerns a number of analytical procedures have been used to determine carbaryl concentrations. 

Aquatic species were also found to be hyperaccumulators in wetland ecosystems (Williams, 2002). Ceratophyllum demersum is described as an arsenic accumulator (Kalbitz and Wenrich, 1998), whereas water hyacinths, Eichhornia crassipes, have been found to be effective in accumulating cadmium, lead, and mercury, and in the uptake of pesticides residues. Duckweed Lemna minor) and water velvet (Azolla pinnata) were both found to effectively remove iron and copper at low concentrations in laboratory experiments, and also cadmium. The yellow water lily (Nuphar variegatum) accumulated copper and zinc. 

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