Simple direct method for the determination of total mercury levels in blood and urine and nitric acid digests of fish by inductively coupled plasma mass spectrometry

Abstract

A simple direct method was developed to determine Hg by ICP-MS in diluted urine, diluted blood and HNO₃ digests of fish. Wash-out times of <130 s for Hg concentrations ≤30 µg l^–1 were achieved by complexing Hg with (NH₄)₂H₂EDTA and the presence of ammonia. A novel disinfection procedure for urine and blood utilised dilution with a virucidal agent, Virkon. Virkon precipitated blood proteins, requiring subsequent dissolution using tetramethylammonium hydroxide. More than 85% of internal QC results were within ±1 µg l^–1 of their target values for blood and >80% within 5% for urine. There was successful participation in three QA schemes for urine and one for blood. NIST Albacore Tuna gave 95% recovery of the target, 0.95 µg g^–1, and good precision, 0.90±0.01 µg g^–1 (n=3). The method did not discriminate between inorganic and organic Hg. Detection limits for Hg, using 3σ at or near the blank level, were 0.13 µg l^–1 in blood, 0.27 µg l^–1 in urine and 0.004 µg g^–1 in fish. The developed methods were used to analyse samples collected from four sites in the Tapajos Valley of Brazil in an EC funded study of exposure to Hg as a result of gold mining. All but one of the subjects (n=106) had Hg levels in either blood or urine that exceeded the upper 95% limits for non-exposed subjects, 55% had blood Hg levels above the 95% limit in industrial workers (19 µg l^–1) and 17% exceeded the urine Hg limit at which industrial workers should be removed from exposure (50 µg l^–1). Subjects living in a fishing village, Jacareacanga, 100 km from mining activities, had significantly higher blood Hg levels (mean 81 µg l^–1) than the other three groups (p<0.004), presumed to be related to fish consumption. Fish Hg levels were similar to those found in other polluted areas, mean 0.379 mg kg^–1 (n=52). The EC study provided the strongest evidence to date in 1991 that Hg in fish in the Amazon basin posed much more of a general health problem than Hg vapour since it affected a larger proportion of the population than just the gold miners, ancillary workers and traders. The methods were also used in the routine clinical analysis of blood and urine samples within the UK National Health Service. Investigations included a case of acute mercury poisoning in a 28-month-old boy who had swallowed a battery who had an initial blood Hg of 394 nmol l^–1 and urine Hg of 16 nmol mmol^–1 creatinine. He was successfully treated with the chelating agent British Anti-Lewisite.