Evaluation of the toxicity of a mixture of dichlorvos and formaldehyde used for mosquito control in Nigeria

Vector control using insecticides (dichlorvos and formaldehyde) is an option in malaria control. This study evaluates the changes in haematological, biochemical, histo-pathological alteration and mutagenic potential induced by the insecticide mixture in albino rats for a period of 2-16 weeks. Haematological examination was done with the aid of an auto-analyser; biochemical assessment of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP), and other parameters was done using standard biochemical procedures. Mutagenicity was assessed, while histopathological examination was done with standard histological preparation. The red blood cell was significantly reduced (p<0.05) in the 12th and 16th week of exposure. There was significant decrease (p<0.05) in the ALT for the 12th and 16th week. Histopathological examination showed congestion, haemorrhage, bronchopneumonia and interstitial inflammation in the lungs, cytoplasmic inclusions in the liver while certain degree of degeneration in the kidney during the early period of exposure and normalcy was restored in the 12th and 16th week. Spermatozoa abnormalities significantly increased (p<0.05) with increase in duration of exposure. The haematological examination showed no significant reduction of the red blood cells in the 12th and 16th weeks, however, there was no serious impact on other blood parameters including kidney and liver. It was observed that the histopathological examination revealed severe impact on the lungs, mild damage to the liver and certain degree of degeneration in the kidney. The mutagenicity study suggests that the mixture may induce mutation. The adverse health implication of locally compounded or mixture of insecticides need to be addressed especially when considering their long term and continuous use in mosquito control.Keywords: malaria, insecticides, biochemical assessment, histopathology, mutagenicity