Toxicity as a Factor Influencing the Distribution of Gammorus Pulex in some Midland Rivers

Abstract

The literature covering river biology, biology of Gammarus pulex, river pollution and toxicity has been reviewed. The Rivers Blythe, Cole, Rea, Tame and tributaries were surveyed to enable distribution maps of Gammarus, Asellus, Chironomidae and Oligochaeta to be drawn. The results of chemical analysis of 24 widespread stations over a 2 year period were used to determine field threshold concentrations. Using the thresholds for copper, zinc, chromium and nickel, a Toxicity Index was calculated, and related to the occurrence of Gammarus. Application to additional sampling stations supported the validity of the method. Analysis on a monthly basis suggested that the Toxicity Index would need to be below 1.0 for at least 70% of the time to allow Gammarus to exist. Laboratory experiments with Gammarus were performed to determine the toxicity of known chanical se These experiments lasted for either 48 hours, or were continued for periods of up to 600 hours, and were used to obtain the 48hrLC50 or threshold values. The effects of water hardness and dissolved oxygen concentration were investigated. Copper, zine and chromium were found to be very toxic, while nickel was shown to be a long-term toxic material. Mixtures of metals were studied and it was confirmed that the toxicity could be predicted from the sum of the toxicities of the components. Application of the laboratory results to the field data gave a field threshold sum of proportions of 0.05, above which Gammarus was absent from the streams studied. This value was examined in relation to literature on fish survival. When related to the laboratory results, after allowing for factors such as water hardness and dissolved oxygen, it would probably account for approximately 5% mortality. The advantages of using Gammarus as a test animal in place of fish are discussed.