Monitoring mercury in two South African herbaria

Mercury [Hg] emissions from old plant collections treated with mercuric chloride (HgCl 2) may present a high health risk for staff working in certain herbaria. The present study evaluated Hg concentrations in ambient air, plant specimens and biological samples from staff working in the Pretoria National Herbarium (PRE) and the H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria. Biological samples from a group of 15 people exposed to HgCl 2 in herbaria and a non-exposed control group of five people were studied. Additionally, plant samples from herbarium specimens treated and non-treated with HgCl 2 were analysed. Plant materials treated with HgCl 2 had persistent high concentrations of Hg in the range of 114–432 µg g − 1 , whereas untreated materials were in the range of 0.20–0.45 µg g − 1 . The HgCl 2-treated plant specimens induced elevated concentrations of Hg into the herbarium rooms near storage cabinets, where up to 1 μg m − 3 of Hg was measured in the air of both herbaria. However, no significant difference in mean Hg concentrations in hair was found between herbarium workers and members of the control group, 0.46 and 0.64 µg g − 1 respectively ( p 0.05, Student's t-test). For both groups, Hg concentrations were lower than that indicated by the World Health Organization [WHO] for non-exposed adults, namely 2 µg g − 1 . The mean concentration of total Hg in urine from the mercury-exposed herbarium group, 2.28 µg g − 1 creatinine, was significantly higher than in the control group, 1.05 µg g − 1 of creatinine. For both populations, the concentrations of Hg in their urine were below the threshold Hg values set by the WHO, i.e., 5 µg g − 1 creatinine. We concluded that there was no strong response by individual herbarium staff from long-term exposure to Hg concentrations in the range of 0.28–1.1 μg m − 3 .