The bioaccessibility of soil-based mercury as determined by physiological based extraction tests and human biomonitoring in children

Abstract

Environmental contaminants associated with soil particles are generally less bioavailable than contaminants associated with other exposure media where chemicals are often found in more soluble forms. In vitro methods, such as Physiological Based Extraction Tests (PBET), can provide estimates of bioaccessibility for soil-based contaminants. The results of these tests can be used to predict exposure to contaminants from soil ingestion pathways within human health risk assessment (HHRA). In the current investigation, an HHRA was conducted to examine the risks associated with elevated concentrations of mercury in soils in the northern Canadian smelter community of Flin Flon, Manitoba. A PBET was completed for residential soils and indicated mean bioaccessibilities of 1.2% and 3.0% for total mercury using gastric phase and gastric+intestinal phase methodologies, respectively. However, as many regulators only allow for the consideration of in vitro results for lead and arsenic in the HHRA process, in vitro bioaccessibility results for mercury were not utilized in the current HHRA. Based on the need to assume 100% bioaccessibility for inorganic mercury in soil, results from the HHRA indicated the need for further assessment of exposure and risk. A biomonitoring study was undertaken for children between 2 and 15 years of age in the community to examine urinary inorganic mercury concentrations. Overall, 375 children provided valid urine samples for analysis. Approximately 50% of urine samples had concentrations of urinary inorganic mercury below the limit of detection (0.1 μg/L), with an average creatinine adjusted concentration of 0.11 μg/g. Despite high variability in mercury soil concentrations within sub-communities, soil concentrations did not appear to influence urinary mercury concentrations. The results of the current investigation indicate that mercury bioaccessibility in residential soils in the Flin Flon area was likely limited and that HHRA estimates would have been better approximated through inclusion of the in vitro study results.

Predicted Mercury Soil Concentrations from a Kriging Approach for Improved Human Health Risk Assessment

“…Although there are many sites with historical mercury contamination, there are only very few studies that assessed the external and internal concentrations to assess mercury-related health risks [ 24 , 25 , 26 ]. None of these studies found association between mercury soil and mercury HBM-values.…”

“…There are many studies, assessing health risks from mercury-contaminated soils using exposure modelling and/or geostatistical methods [ 22 , 23 ]. However, there are very few studies investigating exposures from contaminated soils using HBM and even fewer with individual soil samples [ 24 , 25 , 26 ]. To our knowledge, this is the first study combining HBM, individual soil samples and geostatistical methods in the context of environmental health.…”

Reference Gastrointestinal Absorption Fractions for Radionuclides Ingested in Soil

“…The bioaccessibility of mercury (Hg) in soil has been studied in a variety of soils (Davis et al, 1997;Barnett and Turner, 2001;Neculita et al, 2005;Zagury et al, 2009;Welfringer and Zagury, 2009;Gray et al, 2010;Rodrigues et al, 2014;Safruk et al, 2015;Jiang et al, 2020). Most estimates are well below 10%.…”