Abstract
Heavy metals are chemical elements with a specific gravity that is atleast five times that of water which is 1 at 4 degrees C. The commonly encountered heavy metals are lead,mercury, cadmium, and arsenic. Lead levels in children continue to be a health hazard as the current limit of 10 ug/dL is considered too high with the WHO estimate of 40% of children having blood levels greater than 5 ug/dL. Some authors have suggested a new limit should be set at 2 ug/dL. There are substantial differences in the literature regarding the effects of lead on hearing as assessed by pure tone audiometry. Mercury causes hearing loss and neurological dysfunction in Humans and animals. Methyl mercury is considered a more toxic compound to mercuric chloride. Cadmium causes a range of health effects from lung cancer, kidney damage to hearing loss. Dose dependent effects on hearing loss have been shown in rats. Combined effect with noise exposure has been shown to be more pronounced. Arsenic is released into the environment through the smelting process of copper, zinc, and lead. It is usually found in the water supply. Hearing impairments have been noted in the low and high frequencies in conjunction with balance disturbance.
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