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Two Australian cladocerans, Moina australiensis Sars and a species oi Ceriodaphnia, were evaluated as possible biological indicator organisms to assess the toxicity of irrigation supply and drainage water of the Murrumbidgee and Coleambally Irrigation Areas, M. australiensis, being large (-2000 /um) and orange, was initially chosen to overcome visibility problems in highly turbid Australian inland waters. However, the organism responded erratically in culture. Mortality was high and neonate production was unpredictable when cultured under recommended United States Environmental Protection Agency protocols. Attempts to improve culture performance by optimizing food (quality and quantity), water (control source, hardness, volume) and temperature were only marginally successful. Similar difficulties were not evident when Ceriodaphnia sp, was used as the test organism. Although Ceriodaphnia sp, is small (-1000 /xm), grey and more difficult to see in turbid water its responses were more predictable and reliable than those of M. australiensis. Results of initial trials comparing the two organisms suggest that Ceriodaphnia sp, was a better test organism and more suited to local requirements.

Immunoassays based on microwells (for laboratory assay) and polystyrene tubes (for field assay) have been applied to the analysis of the herbicides, molinate and diuron, in field water samples. Development of a new immunoassay format for molinate, with detection limits of 0.5-1 ppb, enabled, for the first time, the direct analysis of molinate in water samples across the full range of usual field residue levels, without need for pre-concentration. A highly sensitive field assay for urea herbicides (diuron limit of detection of 0.15 ppb) has also been developed, based on a double-layer coating with protein A and urea herbicide-specific antibody. Each assay was only slightly affected by ions and turbidity, which are often problems in subsurface and surface water matrices respectively. For both formats of the molinate and diuron immunoassays, close correlations were obtained between herbicide levels determined by the immunoassay and by instrumental analysis, using field water samples.

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