Short-term oral and dermal toxicity of MCPA and MCPP

The herbicieds 2-methyl-4-chlorophenoxy acetic acid (MCPA) and 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP or mecoprop) were tested for 90 days in rats. The compounds were added to the diet at levels of 0, 50, 400, and 3200 ppm. Growth, food intake, mortality, haematology, blood and liver chemistry, organ weights and histopathology were used as criteria. The main effects of both compounds were growth retardation and elevated relative kidney weights at levels of 400 ppm and more. The 50 ppm dose level can be considered as a no-toxic-effect level in the 90-day study. In subacute dermal studies in rabbits during 3 weeks the dosages were 0, 0.5, 1.0 and 2 g MCPA or MCPP per kg body weight. Therafter followed a recovery period of 2 weeks. Growth, mortality, skin reaction, haematology, organ weights (MCPP) and histopathology were recorded and determined. Both compounds caused slight to moderate erythema at all dose levels, whereas elasticity of the skin was decreased. In both experiments the skin returned to normal during the recovery period. Weight loss was observed at all dose levels. In the MCPA experiment high mortality and histopathological changes in the liver, kidneys, spleen and thymus were recorded at the two highest dose levels. The cause of this could have been either the treatment with MCPA or a dysbacteria infection which developed during the experiment. Oral and intraperitoneal acute toxicity of MCPP for the rat were found to be 1210 and 402 mg/kg, respectively. After a single oral or dermal application of MCPA to the rabbit, the compound was excreted unchanged in the urine.