Maritime Deposition of Organic and Inorganic Arsenic

The speciation of arsenic in wet and dry deposition are ambiguously described in current literature. Presented here is a 2 year study quantifying arsenic species in atmospheric deposition collected daily from an E. Atlantic coastal, semirural site, with comparative urban locations. Inorganic arsenic (As_i) was the principal form of arsenic in wet deposition, with a mean concentration of 0.54 μmol/m³. Trimethylarsine oxide (TMAO) was found to be the dominant form of organic arsenic, determined as above the LoD in 33% of wet deposition samples with a mean concentration of 0.12 μmol/m³. Comparison with codeposited trace elements and prevailing weather trajectories indicated that both anthropogenic and marine sources contribute to atmospheric deposition. Analysis of dry deposition revealed it to be a less significant input to the land-surface for As_i, contributing 32% of that deposited by wet deposition. Dry deposition had a larger proportion of As_i than that found in wet deposition, with TMAO making up only 12% of the sum of species. In comparison, urban sites showed large spatial and temporal variations in organic arsenic deposition, indicating that local sources of methylated species may be likely and that further understanding of biogenic arsine evolution and degradation are required to adequately assess the atmospheric arsenic burden and subsequent contribution to terrestrial ecosystems.