Organophosphorus Pesticide Malathion and Immunotoxicity: A More Sensitive Toxicological Target and Current Recommendations

Background Malathion has been wildly used in agriculture and household pest control for years and can affect human health through drinking water and dietary exposure. This study was to investigate the immunotoxicity of malathion (MLT）on BALA/c mice for the purpose of providing a scientific basis for pesticides registration management of MLT and other pesticides. Methods Female mice were randomly divided into five groups. Both the negative control and the positive control groups of mice were daily gavage with corn oil, and those in the positive control group were intraperitoneal injected with 200 mg/kg bw of cyclophosphamide (CY) 24 h before the end of the study. In the dosage groups, MLT were daily gavage at doses of 16, 65 and 258 mg/kg bw for 30 days, respectively. After exposure, the body weight, the absolute and relative weight of organs, the hematology and clinical chemistry parameters, the splenocyte number, the bone marrow cell classification, histopathology, as well as the cellular immunity, humoral immunity, and non-specific immunity functions of mice were studied. Comparisons between multiple groups were carried out by using one-way ANOVA followed by Bonferroni post hoc comparisons tests when equal variances assumed and Dunnett’s T3 post hoc tests when equal variances assumption was not met.ResultsCompared with the negative control group, the low dose of MLT significantly reduced the levels of IL-10, neutrophil, polychromatic erythroblast and monocyte series (P<0.05)，induced atrophy in white pulp of spleen (1/10), which showed an immunosuppression in mice，and increased the absolute and relative weight of thymus (P<0.05). Inhibition of the PFC response, liver injury and thymus atrophy were observed in the high-dose group. What’s more, the IgG level was abnormally elevated with the increase of dose and presented a dose-response relation (P<0.05). ConclusionsThe immunotoxicity of low-dose of MLT is clear from the evidence and the LOAEL of MLT is preliminarily considered to be 16 mg/kg bw. It is much lower than that of the NOAEL (29 mg/kg bw) based on a 2-year chronic toxicity test and carcinogenicity test in rats, which was used to derive the ADI by Joint WHO/FAO Meeting on Pesticide Residues (0.3 mg/kg bw). It indicates that the immune system is a more sensitive target of MLT toxicity.