Use of Blood Lead and Erythrocyte θ-Amino Levulinic Acid Dehydratase Activity to Detect Lead Exposure of Fish Populations

Abstract

The measurement of blood lead concentrations and inhibition of erythrocyte θ-amino levulinic acid dehydratase activity (ALA-D) has been used successfully to diagnose lead exposure in human populations. While blood lead is one of the best indicators of lead exposure, its measurement is expensive, time consuming, subject to bias through contamination and requires highly skilled personnel. The advantages of assaying ALA-D activity are those of cost, speed, sample size and simplicity. Since most organisms possess this enzyme in a variety of tissues, and since its activity is inhibited only by lead, there is potentially a large variety of aquatic species that may be used to monitor “biologically available” lead in aquatic ecosystems. Sessile and migratory species could integrate short-term fluctuations in waterborne lead and provide data on spatial and temporal variations. Fish are convenient organisms to sample and fish blood is a particularly rich source of ALA-D. Laboratory experiments have defined the optimum conditions for blood sampling and assaying ALA-D activity as well as the strong negative correlation between blood lead concentrations and ALA-D activity and between waterborne lead concentrations and ALA-D activity. Other toxic metals (e.g. Cu, Hg, Zn, Cd) and PCB's do not inhibit ALA-D, and factors that increase lead toxicity (e.g. decreased environmental pH) also increase lead uptake and the inhibition of ALA-D. Consequently, ALA-D activity provides a measure of both exposure and effect. Species variation in rates of lead uptake allows a selection of a suitable monitoring species for a given, situation. Preliminary surveys of Lake Ontario fish populations indicate that monitoring of ALA-D activity is technically simple and straightforward, the assay is much cheaper and faster than blood lead or whole body lead analyses, and activity is correlated to other measures of lead in fish.