The relationship of parathion concentration, exposure time, cholinesterase inhibition and symptoms of toxicity in midge larvae (chironomidae: Diptera)

Larvae of Chironomus riparius were used to demonstrate a statistically significant relationship between four variables: parathion concentration in water (nominally 20 to 500 μg/L), duration of exposure, symptoms of toxicity, and in vivo cholinesterase (ChE) inhibition. The symptoms of toxicity were a series of swimming behaviors that were categorized and assigned numerical values according to intensity of poisoning. These values were correlated with ChE inhibition by a polynomial regression. Therefore, symptoms of poisoning could be mathematically estimated from measurements of percent ChE inhibition. A three-dimensional relationship between ChE inhibition, the logarithm of exposure time, and the logarithm of parathion concentration was established. This permits the characterization of the range of conditions for the onset of a given toxicity symptom and also predicts the symptom for which values for at least two of these variables are provided.