A new study suggests that a holistic approach is needed in assessing the potential environmental and health effects of toxic effluent from industry. The study is published in the International Journal of Environment and Pollution.

Studies of industrial effluent toxicity usually focus on a single contaminant, such as an environmental or marine pollutant, a potential carcinogen, or a toxic heavy metal. However, according to Tatjana Tišler of the National Institute of Chemistry, in Ljubljana, and Jana Zagorc-Koncan of the University of Ljubljana, Slovenia, toxicity tests of effluent using bacteria generally underestimate the total toxicity.

Effluents from industrial or municipal sources may contain hundreds to thousands of chemicals, but only a few are responsible for aquatic toxicity. Simply adding together the individual toxicities of each chemical present is not a reliable way to predict the total toxicity of effluent, the researchers say. An underestimation of whole-effluent toxicity could have seriously detrimental effects on the marine environment.

The researchers point out that the prediction of waste water toxicity usually does not take into account any possible interactions between the compounds in the wastewater sample. The presence of a particular chemical may make another more easily absorbed by aquatic creatures or plants, for instance. Moreover, some highly toxic chemicals may go undetected in a complex waste water mixture.

By testing waste water samples from a tannery, a pharmaceutical plant, and a chemical factory, the researchers were able to demonstrate the presence of key toxic chemicals in the samples and their toxic effects on bacteria, algae, daphnids and fish. Their tests demonstrated a higher toxicity of the whole sample compared with tests carried out on individual pollutants.

"Our results obtained clearly demonstrate the importance of using the ‘whole-effluent’ toxicity approach for a reliable assessment of wastewater quality," the researchers say.