The objective of this study was to use higher plants for detecting effluent toxicity. Eight effluent samples were obtained from three industrial sources prior to their entry into a sewer system. The tests were the duckweed reproduction test, and root growth tests using cabbage and millet. The results of repeated phytotoxicity tests were reproducible. Of the three industrial sources, the effluent samples from a specialty chemical industry were the most toxic. For two samples from this source, the IC50 values (the concentrations which caused 50% inhibitory effect) for duckweed were less than 1.6% effluent concentration. The samples from an agricultural product utilization plant were the least toxic. For these samples, root growth tests failed to obtain IC50 values while the duckweed tests showed IC50 values of 91 and 43% effluent concentration. Among the three types of tests conducted, the duckweed reproduction test showed the greatest sensitivity to effluent toxicity, while root growth tests using cabbage and millet had mixed results. Duckweed is recommended as a part of a battery of tests for effluent toxicity.

The use of phytotoxicity (higher plant) tests as a part of ecotoxicology is relatively underdeveloped. The objective of this study was to evaluate phytotoxicity tests for screening and biomonitoring complex effluent samples. Mortality tests using common duckweed and seed germination tests were conducted using eight effluent samples collected from three industrial sources. Duckweed plants were found to be extremely sensitive to two effluents, with nearly 100% mortality occurring. Duckweed plants in some samples showed lesions (breakup of colony structure) and loss of green pigments (chlorosis); others showed localized dead tissues (necrosis). Six kinds of seeds were tested: cabbage, cucumber, millet, Japanese millet, rice and wheat. Cabbage and millet seeds were the most sensitive. The germination of these seeds was 100% inhibited in some samples. The results suggest that phytotoxicity tests with higher plants have potential for use in the biomonitoring of industrial effluents because of their simplicity, sensitivity and cost‐effectiveness.

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