Effects of nutrient loading and planktivory on the accumulation of organochlorine pesticides in aquatic food chains.

The effects of nutrients and planktivory on the accumulation of hydrophobic organic contaminants (HOCs) in aquatic food chains were investigated in large lake enclosures. Food-chain compositions in the enclosures were manipulated by additions of planktivorous fish (+F), nutrients (+N), both nutrients and fish (+NF), or received no additions (-NF). The treatments resulted in higher plankton but lower zooplankton biomass in the +NF enclosures than in the other enclosures. Once enclosure communities were established, a suite of organochlorine pesticides (alpha-hexachlorocyclohexane, methoxychlor, heptachlor, cis- and trans-chlordane, cis- and trans-nonachlor, and mirex) was added to all enclosures in amounts sufficient to obtain initial concentrations in the epilimnion of approximately 15 ng/L. Dissipation of HOCs from the water and accumulation in phytoplankton, zooplankton, and fish were monitored for four months. The HOC concentrations in plankton did not differ significantly across treatments. However, on a total-mass basis, greater amounts of HOCs were sorbed to phytoplankton in the +NF enclosures (20%) than in the three other sets of enclosures. Concentrations in zooplankton of some HOCs differed significantly between treatments as a function of nutrient loading. Chlordane and nonachlor concentrations were greater in zooplankton from enclosures with no fish (+N, -NF) than in those from enclosures with fish (+F, +NF). The HOC residues in fish were highest in low-nutrient enclosures. The results demonstrate that fish predation and nutrient loading can modify the size-related processes of HOC partitioning and affect its accumulation in the aquatic food chain.