Toxicity assessment due to sub-chronic exposure to individual and mixtures of four toxic heavy metals

Humans are exposed to a cocktail of heavy metal toxicants in the environment. Though heavy metals are deleterious, there is a paucity of information on toxicity of low dose mixtures. In this study, lead (Pb) (0.01 mg/L), mercury (Hg) (0.001 mg/L), cadmium (Cd) (0.005 mg/L) and arsenic (As) (0.01 mg/L) were administered individually and as mixtures to 10 groups of 40 three-week old mice (20 males and 20 females), for 120 days. The study established that low dose exposures induced toxicity to the brain, liver, and kidney of mice. Metal mixtures showed higher toxicities compared to individual metals, as exposure to low dose Pb + Hg + Cd reduced brain weight and induced structural lesions, such as neuronal degeneration in 30-days. Pb + Hg + Cd and Pb + Hg + As + Cd exposure induced hepatocellular injury to mice evidenced by decreased antioxidant activities with marginal increases in MDA. These were accentuated by increases in ALT, AST and ALP. Interactions in metal mixtures were basically synergistic in nature and exposure to Pb + Hg + As + Cd induced renal tubular necrosis in kidneys of mice. This study underlines the importance of elucidating the toxicity of low dose metal mixtures so as to protect public health.