Long range long term transport and decay of PAHs in a semiarid coastal area of Argentina

Abstract

The transport and decay processes of environmental PAHs (Polynuclear Aromatic Hydrocarbons) are important in defining the exposures and risks which they may pose to organisms and man. In southeastern Patagonia, at about 42° S, westerly winds are very active in long range transport of top soil dust and air suspended particulate matter, a phenomenon which is similar to what occurs in other semi‐desert areas of the world. The transport of air suspended particulate around a small town at the atlantic coast of Patagonia was studied by means of a net of continuous monitors (dust gauges and high volume samplers) during 5.5 years. The sampling stations were located at various distances up to about 25 km of a single industrial source which emits PAHs as well as inorganic fluorides at about a constant, continuous and known rate. The concentration of 16 PAHs as well as inorganic F in the dust and in the air, and the rates of advective mass transport per unit of wind erosive power were recorded. The long term analysis of these variables (6‐month moving average regression models) confirms that the emission and dispersion systems have been in relative steady condition during the last years. This simple spatial and temporal situation allows the computation of average long term decay rates of several individual PAHs, by comparing the distribution and transport patterns of these compounds with that of inorganic F‐, which is used as a conservative tracer. A box model of unit angular volumes of the atmosphere centered at the emission source was fitted to the profiles of PAH and F‐concentration at increasing distance from the source. An algorithm to relate spatial rates of decay and transport with temporal rates of decay of several PAHs, based on their known emission rates at the source, is presented. Some PAHs of low molecular weight (<200) were observed to be transported more efficiently than F‐ or heavier PAHs. Environmental decay rates vary from 0.059 g/g/day (Anthracene) to ‐0.62 g/g/day (Fluoranthene), which correspond to half‐lives of 11.5 and 1.1 days respectively. The average half‐life of a group of 12 PAHs investigated is 4.33 days.