New Insights into Health Risk Assessments for Inhalational Exposure to Metal(loid)s: The Application of Aqueous Chemistry Modelling in Understanding Bioaccessibility from Airborne Particulate Matter

Boric acid catalysed hydrolysis of peroxyacids

This study shows for the first time that boric acid catalyses the hydrolysis of peroxyacids, resulting in an approximately 12-fold increase in hydrolysis rate for both peracetic acid (PAA) and 3-chloroperbenzoic acid (MCPBA) when 0.1 M boric acid is present. The maximum rate of hydrolysis occurs at pH 9 and pH 8.4 for PAA and MCPBA respectively. In contrast, carbonate buffer does not enhance the rate of PAA hydrolysis. The reaction was followed by measuring the initial rate of hydrogen peroxide formation using a specific Ti(iv) complexation method. The study of the hydrolysis reaction requires the presence of 2 × 10^-5 M each of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine tetramethylene phosphonic acid (EDTMP) in all solutions in order to chelate metal ions across the full pH range (3 to 13) that would otherwise contribute to peroxyacid decomposition. Catalysis of peroxyacid hydrolysis is most likely effected by the triganol boric acid acting as a Lewis acid catalyst, associating with the peroxide leaving group in the transition state to reduce the leaving group basicity. The products of the reaction are the well characterised monoperoxoborate species and the parent carboxylic acid. Analysis of the pH and borate dependence data reveals that in addition to a catalytic pathway involving a single boric acid molecule, there is a significant pathway involving either (a) two boric acid molecules or (b) the polyborate species, B₃O₃(OH)₄ ^-. Knowledge about catalytic mechanisms for the loss of peroxyacids through hydrolysis is important because they are widely used in reagents in a range of oxidation, bleaching and disinfection applications.

Environmental and human health risk assessment of sulfidic mine waste: Bioaccessibility, leaching and mineralogy

Sulfidic mine waste can pose environmental and human health risks, especially when it contains high levels of mobile metal(loid)s. To assess the environmental and health risks of mine waste originating from three historic and active sulfidic Pb-, Zn- and/or Cu-mines in Europe, mineralogical and chemical characterizations were conducted in combination with in vitro bioaccessibility tests, sequential extractions and leaching tests. Results indicated that most samples contained highly elevated levels of metal(loid)s and key minerals consisting of pyrite, sphalerite and cerussite. The orally bioaccessible fraction varied amongst samples: Cd (13-100%), Zn (9-69%), Pb (4-67%), Cu (8-41%) and As (1-11%). Given these bioaccessible levels, the human health risk assessment indicated carcinogenic and non-carcinogenic risks for most investigated samples in a worst-case exposure scenario. The leaching tests revealed a high mobility of metal(loid)s, especially Pb, posing potential environmental risks. The sequential extractions coupled with mineralogical analyses highlighted the highly mobile levels of Cd, Pb and Zn, posing environmental and health risks. Cerussite dissolved in the easily exchangeable fraction, releasing elevated levels of Pb, while pyrite never completely dissolved. In conclusion, the studied wastes pose environmental and health risks, but the high mobility of some elements also provides opportunities for the valorization of the waste.