A descriptive analysis of blood mercury test results in British Columbia to identify excessive exposures

OBJECTIVE The objective of this study was to describe who in British Columbia (BC) is tested for blood mercury, the distribution of their results, and the adequacy of follow-up testing. METHODS The BC Centre for Disease Control (BCCDC) obtained records of clinician-ordered analyses of blood mercury conducted by BC laboratories during 2009 and 2010. We conducted a descriptive analysis with statistical testing of who was tested, the distribution of their blood mercury concentrations, whose results exceeded Health Canada's proposed guidance values (8 μg/L (40 nmol/L) for children/adolescents ≤ 18 years and women 19-49 years, and 20 μg/L (100 nmol/L) for other adults), and patterns of repeat testing. RESULTS Mercury test results for 6487 individuals were reviewed. Adults ≥ 50 years had the highest testing rates. The median blood mercury concentration for all tested persons was 1.8 μg/L. Nine percent of women aged 19-49 years had results exceeding Health Canada's provisional guidance value of 8 μg/L. Data from one of BC's two biomarker laboratories indicated that some residents of Vancouver and nearby suburbs have higher exposure to mercury than other BC residents. Of 127 individuals who had results in 2009 exceeding provisional guidance values, only 45% were tested again within 12 months. CONCLUSION Collating and analyzing all clinical biomarker testing such as blood mercury at a provincial population level allows for assessment of the adequacy and appropriateness of follow-up testing and suggests which regional and demographic strata are at higher levels of exposure.