Processing of Organic Contaminants in Lakes

Abstract

Toxic organic chemicals are ubiquitous in the aquatic environment resulting from transport to and internal cycling within lake systems. Natural processes occurring in lakes work to remove the toxic chemicals from the water column and possible interaction with biota. The rate of chemical removal processes compared to the rate of input and recycling yields information on the net residence time of toxic chemicals in the lake ecosystem. Chemical contaminants may enter the lake from atmospheric deposition in the form of rain and snow and particle deposition, river inflows, groundwater flow, and direct and indirect discharges from industrial and municipal facilities. Losses of chemicals from the lake occur as a result of incorporation into particles (biotic and abiotic) and subsequent settling, volatilization across the air-water interface, and chemical and biological transformations. The internal processes of resuspension and diffusion of bottom sediments and porewater may release chemicals into the water column reducing the net loss rate in the lake. The chemicals treated here are the hydrophobic organic contaminants (HOCs) characterized by their ability to partition into biotic pools as a result of their low aqueous activities and general resistance to chemical and biological degradation. Examples of hydrophobic organic chemicals (HOCs) are the polychlorinated biphenyls (PCBs), the organochlorine (OCs) pesticides such as p,p’-DDT and lindane (g-HCH), and the polynuclear aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (B[a]P).