Biological monitoring and exposure to mercury

Occupational health professionals' interest in controlling mercury (Hg) exp osure, and the use of biological monitoring in this context, has been ongoi ng for a number of years. Evidence from urinary Hg results in a number of U K firms who have undertaken some form of biological monitoring or occupatio nal health surveillance suggest that exposure has decreased over the last 1 0-15 years. This decrease precedes the establishment in the UK of an adviso ry biological monitoring guidance value (HGV) for urinary Hg and the produc tion of updated medical guidance from the Health & Safety Executive on Hg e xposure (MS12 1996). This latter document recommends a urinary sampling int erval for urinary Hg of between 1 and 3 months, which is consistent with th e reported toxicokinetics of Hg excretion, but we highlight that urinary Hg represents integrated exposure over many previous months. Mercury is a rec ognized nephrotoxin and MS12 1996 mentions the use of regular dipstick prot ein estimations. We review our experience of investigating proteinuria and enzymuria in a large-scale cross-sectional occupational study. The incidenc e of Hg-induced renal disease is probably very rare at current exposure lev els. Therefore acceptance of a high false-positive rate of proteinuria not related to Hg exposure needs to be considered in any urinary protein testin g regime of Hg workers. The establishment of an HGV for urinary Hg has rais ed questions about the uncertainty associated with a urinary Hg result, inc luding factors such as diurnal variation, whether urine correction by creat inine or specific gravity is preferable and the possibility of non-occupati onal sources of Hg contributing significantly towards breaching the HGV. Co rrection of urinary Hg results by creatinine or specific gravity and the us e of a fixed sampling time, such as the beginning or end of the day, substa ntially reduce the uncertainty in a urinary Hg measurement. But even with g ood laboratory precision, an individual with a true urinary Hg excretion of 20 nmol/mmol creatinine could supply urine samples of between 14 and 26 nm ol/mmol creatinine. The influence of dietary sources in the UK contributing to urinary Hg values approaching or exceeding the HGV is unlikely. The use of tribal or ethnic cosmetics and remedies needs to be considered if a uri nary Hg result looks inappropriately high, as some such preparations have b een found to contain Hg and can be absorbed through the skin. The ability o f excessive chewers or teeth grinders who have a large number of dental ama lgam fillings to breach the urinary HGV in the absence of substantial occup ational Hg exposure has been reported in a few Scandanavian studies. We rep ort here a likely case of this phenomenon. Since the establishment of the H GV, our biological monitoring Hg data from a number of industry sectors usi ng inorganic or metallic Hg have suggested that a minority of samples (13%) are still greater than the HGV.