Active biomonitoring in freshwater environments: early warning signals from biomarkers in assessing biological effects of diffuse sources of pollutants

Abstract

This paper presents results from a field study in the Rietvlei Wetland system, Gauteng, South Africa using the freshwater mollusk and freshwater fish as bioindicator organisms. Active biomonitoring (ABM) exposures were conducted where organisms were exposed for 28 days in an effluent dominated river during high flow conditions. The river receives effluent from a wastewater treatment plant and an industrial complex, so that up to 75%, of the total flow of the river is effluent-based. Effluents are a main source of direct and continuous input of pollutants in aquatic ecosystems; the study of the effects of effluent exposure on organisms has a high ecological relevance. However due to the unknown and complex nature of effluents it is virtually impossible to relate observed effects to specific pollutants or even a class of pollutants. Effects of field exposure were determined using cellular biomarkers for example DNA damage, HSP 70, metallothionein, acetylcholine esterase, lactate dehydrogenase and ethoxyresorufin-o-deethylase activity. The results indicated that although the traditional mortality-based whole effluent toxicity testing did not designate any toxicity, the in situ exposed organisms were stressed. A multivariate statistical approach was particularly useful for integrating the biomarker responses and highlighting sites at which more detailed analysis of chemical contamination would be useful. Based on the individual biomarker results contributing towards the distinct groupings it is possible to conclude that Site I is subjected to organic pollutants, whereas Sites 2 and 3 undergo a combination of metallic and organic pollutant stress. However, it is essential that a rapid and sensitive biomarker that is representative of the responses of a suite of biomarkers be tested before ABM can be implemented as a routine biomonitoring practice in water resource management.