A quantitative index of synergism, anatagonism and additivity has been measured experimentally in the fish Mystus vittatus for three pesticides viz. Thiotox (Endosulfan) (T), Dichlorvos (D) and Carbofuran (C). For a combination of two pesticides, the dose of the one pesticide of a pair was fixed at the no-effect level while the dose of the second pesticide was increased until the entire dose response curve was obtained. To evaluate interactions of three pesticides, the previous pair of pesticides was kept fixed at their combined TL(,0) level, and the third pesticide was increased and again a dose-response curve was obtained. From the results obtained, it is shown that a particular combination could be synergistic, antagonistic or additive, depending on the relative doses employed. In the present study (T + D)/C combination was most synergistic (toxic) in nature while D/T and C/T were least toxic antagonistic in their effects. However, T/D, (C + T)/D, C/D and D/C combinations were additive in nature. (D + T)/C, (D + C)/T, (T + C)/D and (C + D)/T combinations were found less synergistic in nature than (T + D)/C.

A simple marine algal bioassay method is described for short- and long-term studies on pesticides and industrial wastes. It can be used for rapid screening of a variety of substance with single-species and multiple-species tests and gives relative toxicities of the pollutants tested. Algae are grown in optically matched culture tubes that fit directly into spectrophotometer, allowing population density to be estimated by absorbance without removal of samples. 96h EC50 values for some pesticides and the diatom Skeletonema costatum are: EPN, 340 micro-g/l; carbophenothin, 109 micro-Gg/l; DEF,366 micro-g/l; ethoprop, 8.4 micro-g/l; methylparathion, 4.3 micro-g/l, and phorate, 1.3 micro-g/l. Presence of the chelator EDTA in medium had no effect on toxicity of carbaryl to S. costatum, Nitzschia angularum, Chorococcum sp. and Chlorella sp. Liquid industrial wastes either stimulated growth, inhibited growth, or stimulated growth at low concentrations but inhibited it at higher concentrations. In mixed species studies with the herbicide neburon, presence of a resistant species protected the sensitive species. Liquid industrial wastes from a paper products plant caused changes in relative numbers, as compared to controls, when S. costatum and Porphyridium cruentum were grown together.