ANALYTICAL VALIDATION OF AN APPARATUS FOR VOLATILE ARSENIC-TRAPPING

Arsenic (As) is considered the most toxic xenobiotic according to the Agency for Toxic Substances and Disease Registry1. However, As toxicity depends on its chemical form. Indeed, inorganic As (As3+ and As5+) are highly toxic while methylated As compounds can be either less or more toxic than inorganic As. Furthermore, the toxicity of volatile As species is mostly unknown. Arsenic bio volatilization occurs in several environments such as soils and rivers sediments, however only few studies are available due to the lack of quantitative methods for As-trapping. Nowadays, methods of capture of volatile species of As have been developed. However, in Brazil, there is still no data on methodologies and evaluation of As bio volatilization. Thus, the present work aimed to validate an apparatus for volatile As trapping such arsine (AsH3), mono-, di- and trimethyl arsines (AsH2(CH3), AsH(CH3)2 and As(CH3)3) based on previous study of Mestrot et al.2. The glass apparatus developed was composed by a modified Erlenmeyer with 2 spouts: a-) one side capped entrance for reagent addition and; b-) one superior to fit two glasses ducts which conduct the filtered atmospheric air inside and other for the outlet of the gases produced in the Erlenmeyer (volatile As). For As-trapping, a tube containing silica gel impregnated with AgNO3 1 % m/v was connected at the end of the outlet duct. The Ag+ promotes the oxidation of AsH3 (AsH3(g) + Ag+(aq) → As2O3(s) + Ag0(s)). The tests for validation were performed by using the hydride generation (NaBH4 1% m/v, HNO3 10% v/v and H3AsO4). All analysis were performed by an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7900, Japan). Our results showed that the aspiration 60 mL min-1 recovered 75% (375.2 ng) of the As. Tests using N2(g) instead of atmospheric air showed that no significant oxidation is promoted by the oxygen present in the atmospheric air. In order to know the trapping efficiency of different volatile As-species, AsH2(CH3) and AsH(CH3)2 were produced. The concentrations for the different species were 200, 550 and 750 ng g-1, respectively. We observed recovery of 90% for all species with no de-methylation (AsH(CH3)2 → AsH2(CH3) → As5+). Next studies will focus on the application for environmental As bio-volatilization for novel biogeochemical cycle information.