Organochlorine dynamics between zooplankton and their environment, a reassessment

Abstract

The level of organochlorine contamination in estuarine, coastal or oceanic waters and various depth strata, including surface films, is important in predicting bioaccumulation in zooplank-ton. Present and past levels of contamination in seawater are briefly reviewed and summarized. Most of the evidence indcates that little organochlorine is truly dissolved in seawater: most molecules are sorbed onto particulate material or sequestered into rnicellar structures. A first-order l n e t i c model is adequate to describe the accumulation of organochlorines by zooplankton from seawater because current laboratory techniques are not refined enough to disbnguish pathways within the organism. The chemical nature of the compounds, such as chlorine content, influences the time taken to reach an equilibrium level in an organism and the bioaccumulation at equilibrium. Size of organism, and temperature and salinity of the environment affect organochlorine uptake rates; this is believed to be related to the weight-specific surface area of the zooplankter exposed per unit time. The lipid content influences the carrying capacity of the zooplankter or its bloconcentration factor from seawater The same kinetic model can be expanded to include organochlorines asslmllated through feeding on contaminated food. Experimental studies have shown that 'field' levels of contamination in zooplank-ton can be reached in the lab within days by accumulation from food. The transfer of organochlorines from generation to generation in the lipid-nch eggs of zooplankters is discussed and explored with the l n e t i c model. Juvenile stages are prehcted to contain the highest organochlorine levels after yolk absorption and therefore should expenence the greatest n~ortality. Finally, it is concluded, from consideration of present levels of contamination, that the water column is the present and probably ultimate repository of most organochlorine compounds in the marine environment and that zooplank-ton play a major role in distributing organochlorines from atmospheric 'fallout' throughout the ocean depths.