Inter- and intraspecific variation in sensitivity to toxins; the effects of acidity and zinc on the freshwater crustaceans Asellus Aquaticus (L.) and Gammarus pulex (L.)

Sensitivity to pH and zinc is compared between species of freshwater crustaceans, within species between size classes, and within size classes and species between populations. Variation is recorded at all these levels. Asellus aquaticus is more tolerant than Gammarus pulex. Small size classes are generally less tolerant than large. Individuals from populations in polluted sites are more tolerant than those from populations in cleaner sites.