PrNo, P. C. ,rNo Peul, E. A. 1980

Distillation was re-evaluated for the formation of artifacts arising from increasing naturally occurring mercury(II) concentrations, as opposed to previous identification of artifacts by spiking standard mercury(II) into samples. Naturally occurring mercury(II) concentrations lower than 2 µg g −1 were found not to affect methylmercury (MeHg) results. However, when the natural concentrations of mercury(II) were greater than 2 µg g −1 , in contrast to standard mercury(II) spiked in samples, the MeHg concentrations measured were found to decrease (not increase) with increasing naturally occurring mercury(II) concentrations. This indicated that standard mercury(II) spiked in samples behaved differently from naturally occurring mercury(II) in the formation of MeHg artifacts during distillation. As a result, spiking standard mercury(II) into samples to identify the formation of MeHg artifacts is not adequate. It is difficult to explain why high naturally occurring mercury(II) suppresses MeHg measurements during distillation. In comparison with HNO 3 leaching/solvent extraction (and other existing techniques), distillation was found to generate results comparable for samples containing less than 2 µg g −1 mercury(II). The HNO 3 leaching/solvent extraction showed significant advantages over other procedures, as this technique generated the highest recoveries with good precision for all samples analyzed, and the results were found to be independent of mercury(II) concentrations for both naturally occurring and spiked standard mercury(II). Thus, except for samples from high mercury-contaminated fields, distillation is still a good choice. Both the positive bias (possibly caused by artifact formation of MeHg) and the negative bias (due to incomplete leaching, back-adsorption, and/or decomposition of MeHg) were investigated. Geologically, physically, and chemically different samples were used for the investigation.

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Because trace amounts of mercury in crude oil can produce negative impacts on refinery operations and profitability, and thus affect oil's quality and price, accurate determination of mercury using a reliable technique is very important. Since its development in 1995, the combustion/trap technique has been continuously improved and employed to generate accurate results for the refinery industry, and showed significant advantages over wet extraction methods. The analytical performance of the combustion/trap technique in different types of samples at different mercury concentration levels was statistically compared with wet extraction methods. The statistical comparison would help refiners and analytical chemists in understanding and choosing an adequate technique for analysis of crude oil and various refinery products, and help in assessing existing analytical results obtained using different techniques. Comparison of results indicated that wet extraction methods could generate negative bias of up to 50%, depending on different types and concentration levels of samples. Negative bias found for oil samples can hide potential risks caused by mercury poisoning to some critical refining operations which require processing of oils free of mercury. The combustion/trap technique can be used for analysis of all crude oils and various refinery products except sulfur, while wet extraction methods cannot be used for analysis of most refinery products.

Nine years after thinning (removal of 2/3 of the basal area) and fertilization (at 448 kg N ha−1, applied as urea), 34-year-old Douglas-fir trees (Pseudotsugamenziesii (Mirb.) Franco) were destructively sampled. The dry weights of seven aboveground components were determined and regression equations from dbh were developed. Differences among treatments were shown for all biomass components and the proportions of the total biomass allocated to the various components. Specifically, thinning decreased the proportion of biomass allotted to wood, bark, and dead branches, while increasing the proportions in foliage and live branches; fertilization increased the proportion of biomass in branches, but had negligible effects on the proportions of other components.