sexta-feira, 27 de novembro de 2009

Das qualidades da água



Já conhecíamos a água gaseificada mas, no Seixal, temos também água "polvorizada". Esta é a preocupante conclusão de um trabalho realizado por investigadores suíços e portugueses sobre a qualidade da água nos aquíferos situados na área envolvente da antiga fábrica da Pólvora. As conclusões não animadoras, embora os responsáveis da câmara, fiéis ao seu estilo de "tudo vai bem, no melhor dos concelhos possíveis", se tenham apressado a desvalorizar ...
"[...] The groundwater residence times were distinctly different in the two aerobic aquifers, as determined by the tritium (3H)–3He method. In the contaminated zones, the upper aquifer exhibited groundwater ages of 25 years, whereas the lower (presumably confined) aquifer contained hardly any tritium which indicates water ages >55 years. P-NACs-containing waste waters are known to have leaked into the upper, unconfined aquifer. However, P-NACs were present in both aquifers in high concentrations (up to 33 000 μg L−1 TNT), which implies a hydraulic connection, although tritium concentrations and chemical data suggest two separated aquifers. Based on the 3H–3He groundwater dating and the presence of very high P-NAC concentrations, the contamination of the lower aquifer must have happened during the early stage of the explosive production, i.e. >50 years ago. Despite this ‘old’ contamination, TNT and DNT have not been transformed until to date as is demonstrated by the negligible changes in their carbon isotopic signatures (δ13C). Thus, P-NACs are very recalcitrant to degradation at the investigated site. If the aquifers remain aerobic, TNT and DNT are expected to persist in the subsurface for many decades to centuries.
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