Biological monitoring of low level exposure to toxic metals (cadmium and mercury) – new challenges for risk assessment

While the knowledge about appropriate biomonitoring and analytical methods are well established at moderate or high exposure to toxic metals, there are many challenges at low-level exposure.    Urinary cadmium has a long tradition as indicator of kidney cadmium and body burden of cadmium. There are, however, potential problems in interpretation at low level exposure; confounding by smoking or urinary flow rate, as well as the possible co-excretion of cadmium and proteins. The relation between urinary cadmium and kidney cadmium may not be linear. The risk assessment at low-level cadmium exposure has mainly been focused on the kidneys. At environmental exposure there is now increased concern about other potential adverse health effects, such as low bone mineral density and fractures, hormone-related cancer, and possibly cardiovascular disease. This should be taken into account at occupational exposure. In addition to exposure biomarkers, the effects of cadmium are usually evaluated using biomarkers, and there is a continuous development of markers of effects on kidney and bone.    Urinary mercury as indicator of long term exposure and blood mercury reflecting also recent exposure are well established biomarkers for occupational exposure to mercury vapor. At low level occupational exposure, the contribution from environmental exposure from fish and/or dental amalgam will contribute substantially to mercury levels. The use of several media (urine, blood, hair), or speciation, can help differentiate the sources. Several nutrients in fish, as well as good dental health, are beneficial for cardiovascular health. On the other hand, methyl mercury (from fish) may increase cardiovascular risk. This must be taken into account when using mercury levels in risk assessment of low level occupational or environmental exposure.