Long term air quality monitoring of trace toxic pollutants in the area surrounding a WtE plant.

An experimental investigation for evaluating environmental levels of the most significant toxic trace compounds of waste incineration interest, including both heavy metals (As, Cd, Hg, Ni, Pb) and organic substances (PCDD/Fs, PAH), was performed over a yearly period. Sampling was performed at three locations in the surrounding area of a WtE plant, selected to be representative of different exposure situations to its emissions: higher expected source impact, industrial contribution from an area aside the eastern boundary of the plant and a reasonable background condition in a residential urban at nearly 8 km from the plant, along a direction not affected by prevailing winds for most of the year. Measurements were performed with biweekly duration for two different seasonal periods of the same year (winter and summer), and involved As, Cd, Ni, Pb on PM10, gaseous Hg and PAHs and PCDD/Fs. Trace metals data observed result in concentration largely included in the few ng/m3 range of values, with frequent episodes arising in results below to detection limits of sampling and analytical procedures applied (0.5 ng/m3) and slight slightly more significant levels for Ni and Pb, despite still remaining at comparable small magnitudes. All measurements are affected by contained variations between seasonal campaigns, with no clearly identifiable behavior, whilst they result mostly essentially comparable for different sites. For organic species PAHs results, analyzed in terms of benzo(a)pyrene as the most toxic member of the whole mixture, are similarly included in lower range of concentrations, with higher winter values between 0.1 and 0.9 ng/m3 around winter samplings and any detectable value during summer sampling (< 0.02 ng/m3); same pattern is observed for all the other PAH species measured, without particular differences between sites. Increase in levels obtained for winter conditions has to be considered to be typical for similar areas, where residential heating with small wood combustion appliances is extensively utilized. For PCDD/F family of pollutants, during summer conditions all the congeners were not detectable at any site (< 0.005 pg/m3), with levels in winter located at the lower fgI-TEQ/m3 range, included around 18 to 23 fgI-TEQ/m3 and still with any significant and relevant difference between sites. Finally, the comparative examination of actual investigation with similar periodic monitoring exercises, conducted previously in the area for same or similar sites from almost 15 years ago, result in yearly variations of the pollutants measured contained in a relatively narrow range of values, with the latest actual measurements frequently located near the lower bound of available data. Consequently, the absence of significant observable trends towards long-term variations in the main trace pollutants associated with waste-to-energy activity should be considered an important element for evaluating the lack of a systematic contribution of the investigated plant.