Lead speciation in indoor dust: a case study to assess old paint contribution in a Canadian urban house

Residents in older homes may experience increased lead (Pb) exposures due to release of lead from interior paints manufactured in past decades, especially pre-1960s. The objective of the study was to determine the speciation of Pb in settled dust from an urban home built during WWII. X-ray absorption near-edge structure (XANES) and micro-X-ray diffraction (XRD) analyses were performed on samples of paint (380–2,920 mg Pb kg⁻¹) and dust (200–1,000 mg Pb kg⁻¹) collected prior to renovation. All dust samples exhibited a Pb XANES signature similar to that of Pb found in paint. Bulk XANES and micro-XRD identified Pb species commonly found as white paint pigments (Pb oxide, Pb sulfate, and Pb carbonate) as well as rutile, a titanium-based pigment, in the <150 μm house dust samples. In the dust fraction <36 μm, half of the Pb was associated with the Fe-oxyhydroxides, suggesting additional contribution of outdoor sources to Pb in the finer dust. These results confirm that old paints still contribute to Pb in the settled dust for this 65-year-old home. The Pb speciation also provided a clearer understanding of the Pb bioaccessibility: Pb carbonate > Pb oxide > Pb sulfate. This study underscores the importance of taking precautions to minimize exposures to Pb in house dust, especially in homes where old paint is exposed due to renovations or deterioration of painted surfaces.     

A rational procedure for estimation of greenhouse-gas emissions from municipal wastewater treatment plants.

Municipal wastewater treatment may lead to the emission of greenhouse gases. The current Intergovenmental Panel on Climate Change (Geneva, Switzerland) approach attributes only methane emissions to wastewater treatment, but this approach may overestimate greenhouse gas emissions from the highly aerobic processes primarily used in North America. To better estimate greenhouse gas emissions, a procedure is developed that can be used either with plant-specific data or more general regional data. The procedure was evaluated using full-scale data from 16 Canadian wastewater treatment facilities and then applied to all 10 Canadian provinces. The principal greenhouse gas emitted from municipal wastewater treatment plants was estimated to be carbon dioxide (CO2), with very little methane expected. The emission rates ranged from 0.005 kg CO2-equivalent/m3 treated for primary treatment facilities to 0.26 kg CO2-equivalent/m3 for conventional activated sludge, with anaerobic sludge digestion to over 0.8 kg CO2-equivalent/m3 for extended aeration with aerobic digestion. Increasing the effectiveness of biogas generation and use will decrease the greenhouse gas emissions that may be assigned to the wastewater treatment plant.     

Joint action of ozone and hydrogen fluoride on foliar senescence in maize

Maize (Zea mays, L.) plants were exposed intermittently to O(3), HF or both pollutants and the progression of foliar senescence was followed by measuring chlorophyll loss, membrane breakdown and changes in stomatal conductance. At concentrations insufficient to cause foliar symptoms (0.06 microl O(3) litre(-1) and 1.0 microg Fm(-3)), exposures to HF had little or no effect, whereas O(3) exposures accelerated the rate of senescence. The rapid rate of senescence produced by O(3) was moderated if the plants were also exposed to HF. Topical application of 6-benzyladenine (BA) prior to pollutant exposures delayed senescence in all plants and completely prevented the O(3)-induced acceleration of senescence.