Assessment of the acute toxic effects of the fungicide Ridomil plus 72 on aquatic organisms and soil micro-organisms

The acute toxic effects of Ridomil plus 72 (Ridomil), used as a fungicide i n agriculture, were studied under laboratory conditions. These effects on f reshwater cladoceran (Chydorus eurynotus) and freshwater fish (Oreochromis niloticus) were determined using standard bioassay procedures. The 4 h LC50 for Chydorus eurynotus was 6.9 mg/L and the 96 h LC50 for Oreochromis nilo ticus was 1.1 mg/L. The toxicity of Ridomil to a mixed population of soil m icro-organisms was measured using oxygen uptake and growth as measured by t urbidity. At short-term exposure (48 min), Ridomil was moderately toxic to the culture at 5000 mg/L and above, based on an activity quotient (AQ) of 0 .50-0.70. For longer exposure periods (up to 6 h), Ridomil was slightly tox ic to the culture at 200 to 500 mg/L. At 1000 mg/L, Ridomil was moderately toxic and at 3000 mg/L and above, Ridomil was extremely toxic to soil micro organisms. The toxicity of metalaxyl tone of the two active ingredients of Ridomil) to these micro-organisms was measured using growth as measured by the turbidity change. The average toxic endpoint (16 h IC50) was 1100 mg/L. The acute toxic values of Ridomil found in these studies were much below t he expected environmental concentrations resulting from normal applications of the chemical on a cocoa tree as a fungicide. (C) 2000 by John Wiley & S ons, Inc.