Sample storage and extraction efficiencies in determination of polycyclic and nitro musks in sewage sludge

Analytical technology is continuously improving, developing better methods for isolating and concentrating trace compounds in environmental samples. Polycyclic and nitro musks (PNMs) are one group of emerging trace compounds detected in municipal wastewater. Differences in sample storage, preparation, and extraction methods for their measurement have led to variability in results. We analyzed 11 PNMs by GC/MS and compared the results of different storage times and extraction methods (supercritical fluid (SFE) or microwave-assisted (MAE)) for 202 samples of primary sludge, waste activated sludge (WAS), raw sludge, and aerobically/anaerobically digested biosolids collected from Canadian municipal wastewater treatment plants. Sixty-three air-dried samples were extracted by SFE, and 139 air-dried, centrifuged, or filtered samples were extracted by MAE. The mean surrogate recoveries were 89% (standard deviation (SD)=11%) for d(10)-anthracene by SFE and 88% (SD=14%) for d(10)-phenanthrene by MAE. Storage study results showed that PNM concentrations changed by a mean of 7% and 9% for primary sludge and WAS respectively after four weeks and decreased up to 25% after 13.5 months of storage in amber glass containers at -18 degrees C. Air-drying of sludge at room temperature caused losses of about 50% of PNM concentrations compared to centrifugation. The proportions of PNMs present in the liquid phase of sludge samples were less than 5% compared to proportions in the sludge solids. The most complete liquid-solid separation was achieved by filtration of frozen/thawed sludge samples, producing a liquid phase that contained less than 1% of the total musk content of the sample.     

Sampling strategies for water quality monitoring in lakes: the effect of sampling method

Five different water sampling techniques have been compared in a series of lakes. In deep lakes, no significant differences were observed between mean summer nutrient concentrations measured in (i) a tube sample integrating over the photic zone taken from the deepest point; (ii) a surface dip sample taken at the deepest point; (iii) a surface dip sample taken by wading into the water's edge; (iv) a dip sample taken slightly further off shore by suspending a bottle below a buoy thrown out about 30 m from the shore; and (v) a sample taken along a short transect out from the shore using a model boat to transport the sample bottle. In shallower lakes the integrating tube sampler gave significantly higher estimates of mean concentrations than other methods due to the increase in volume of the unmixed hypolimnion which reduced the depth of the well mixed epilimnion to less than the tube length. For national survey purposes samples taken from the edge of the lake are the most cost effective.