Determination of uptake rate constants for six organochlorines in midge larvae

Various methods are used to measure the residue-forming potential of organic chemicals in aquatic organisms. The majority of these studies have been conducted with fish and rely on the determination of steady-state partitioning, a method that is expensive, both in terms of time and analytical cost. The midge (Chironomus riparius) is readily available, easily cultured and provides an alternative system with which to study chemical uptake. To evaluate this system, the uptake rate constants of six organochlorines were determined under nonequilibrium conditions, using the midge.

Uptake rate constants were calculated from uptake data using a first-order kinetic expression. Significant correlations were found between the uptake constants of the six chlorinated hydrocarbons and their water solubility and octanol/water partition coefficient values. Multiplying the uptake constants by their molecular weight provided values that were highly correlated with log octanol/water partition coefficients (r² = 0.93) and log aqueous solubility (r² = 0.97) when analyzed by linear regression. Using the midge, uptake constants can be determined in a short time and may be used to make reliable predictions about the relative penetrating power of many chemicals in aquatic invertebrates.