Effects of pH and feeding regime on methylmercury accumulation within aquatic microcosms

The effect of pH (pH 5, 6 or 7) on accumulation of radiolabelled methylmercury was examined using a laboratory microcosm system. Accumulation of labelled mercury at three trophic levels, primary consumers (Daphnia magna), secondary consumers (rainbow trout, Salmo gairdneri) and tertiary consumers (walleye, Stizostedion vitreum) was not significantly affected by pH. Our results are in direct contrast with field observations of elevated methylmercury concentrations in fish from low pH water and indicate that the elevated mercury residues observed in the field result from factors other than the direct effects of pH on accumulation of methylmercury by aquatic organisms. Both water and diet were important as sources of the labelled mercury which was accumulated by walleye. Walleye which were fed rainbow trout, that had accumulated labelled mercury from within the experimental microcosms, accumulated almost twice as much labelled mercury as walleye fed non-labelled prey, or walleye which were not fed. Walleye fed non-labelled rainbow trout accumulated slightly more labelled mercury than walleye which were not fed, presumably as a result of the higher metabolic rate of the fish which were fed.     

Application of the tracer-aerosol gradient interpretive technique to sulfur attribution for the big bend regional aerosol and visibility observational study

A simple data analysis method called the Tracer-Aerosol Gradient Interpretive Technique (TAGIT) is used to attribute particulate S and SO2 at Big Bend National Park in Texas and nearby areas to local and regional sources. Particulate S at Big Bend is of concern because of its effects on atmospheric visibility. The analysis used particulate S, SO2, and perfluorocarbon tracer data from six 6-hr sampling sites in and near Big Bend National Park. The data were collected in support of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study; the field portion was conducted from July through October 1999. Perfluorocarbon tracer was released continuously from a tower at Eagle Pass, TX, approximately 25 km northeast of two large coal-fired power plants (Carbon I and II) in Coahuila, Mexico, and approximately 270 km east-southeast of Big Bend National Park. The perfluorocarbon tracer did not properly represent the location of the emissions from the Carbon power plants for individual 6-hr sampling periods and attributed only 3% of the particulate S and 27% of the SO2 at the 6-hr sites in and near Big Bend to sources represented by the tracer. An alternative approach using SO2 to tag "local" sources such as the Carbon plants attributed 10% of the particulate S and 75% of the SO2 at the 6-hr sites to local sources. Based on these two approaches, most of the regional (65-86%) and a small fraction (19-31%) of the local SO2 was converted to particulate S. The analysis implies that substantial reductions in particulate S at Big Bend National Park cannot be achieved by only reducing emissions from the Carbon power plants; reduction of emissions from many sources over a regional area would be necessary.     

Odours from pulp mill effluent treatment ponds: the origin of significant levels of geosmin and 2-methylisoborneol (MIB)

Pulp and paper mills are well known for their sharp, sulphurous stack emissions, but the secondary treatment units also can be significant contributors to local odour. This study investigated the source(s) of earthy/musty emissions from a mixed hardwood pulp mill in response to a high local odour. Samples from five sites in the mill over five months were analyzed for earthy/musty volatile organic compounds (VOCs), examined microscopically, and plated for bacteria and moulds. In all cases, activated sludge showed substantial geosmin levels and to a lesser extent 2-methylisoborneol (MIB) at 2000-9000 times their odour threshold concentrations (OTCs). These VOCs were lower or absent upstream and downstream, suggesting that they were produced within the bioreactor. Geosmin and MIB were highest in late summer and declined over winter, and correlated with different operating parameters. Geosmin was most closely coupled with temperature and MIB with nitrogen uptake. Cyanobacteria were present in all sludge samples, but actinomycetes were not found. Gram-negative bacteria and one fungal species isolated from the bioreactor and secondary outfall tested negative for geosmin or MIB. We conclude: (i) geosmin and MIB contribute significantly to airborne odours from this mill, but are diluted below OTC levels at the river; (ii) these VOCs are generated by biota in the activated sludge; and (iii) cyanobacteria are likely primary source(s). The growth of cyanobacteria in activated sludge represents a loss of energy to the heterotrophic population; thus earthy/musty odours may represent a diagnostic for less than optimal conditions.     

PM2.5 and PM10 Concentrations from the Qalabotjha Low-Smoke Fuels Macro-Scale Experiment in South Africa

This article presents results from the particulate monitoringcampaign conducted at Qalabotjha in South Africa during the winter of 1997. Combustion of D-grade domestic coal and low-smoke fuels were compared in a residential neighborhood to evaluate the extent of air quality improvement by switchinghousehold cooking and heating fuels.Comparisons are drawn between the gravimetric results from the two types of filter substrates (Teflon-membrane and quartz-fiber) as well as between the integrated and continuous samplers. It is demonstrated that the quartz-fiber filters reported 5 to 10% greater particulate mass than the Teflon-membrane filters, mainly due to the adsorption of organic gases onto the quartz-fiber filters. Due to heating of sampling stream to 50 °C in the TEOM continuous sampler and the high volatile content of the samples, approximately 15% of the particulate mass was lost during sampling.The USEPA 24-hr PM_2.5 and PM₁₀ National Ambient Air Quality Standards (NAAQS) of 65 g m^-3 and 150 g m^-3, respectively, were exceeded on several occasions during the 30-day field campaign. Average PMconcentrations are highest when D-grade domestic coal was used, and lowest between day 11 and day 20 of the experiment when a majority of the low-smoke fuels were phased in. Source impacts from residential coal combustion are also found to be influenced by changes in meteorology, especially wind velocity.PM_2.5 and PM₁₀ mass, elements, water-soluble cations (sodium, potassium, and ammonium), anions (chloride, nitrate, and sulfate), as well as organic and elemental carbonwere measured on 15 selected days during the field campaign. PM_2.5 constituted more than 85% of PM₁₀ at three Qalabotjha residential sites, and more than 70% of PM₁₀ at the gradient site in the adjacent community of Villiers. Carbonaceous aerosol is by far the most abundant component, accounting for more than half of PM mass at the three Qalabotjha sites, and for more than a third of PM mass at the gradient site. Secondary aerosols such as sulfate, nitrate,and ammonium are also significant, constituting 8 to 12% of PM mass at the three Qalabotjha sites and 15 to 20% at the Villiers gradient site.     

Comparison of PM10 concentrations in high- and medium-volume samplers in a desert environment

The USEPA replaced TSP with PM₁₀ as the National Ambient Air Quality Standard for particulate matter. The commercially available PM₁₀ sampler is a high-volume model using quartz fiber filters. In certain investigations, such as source apportionment studies, chemical analysis of the filter is necessary, however, many analyses cannot be run on quartz filters. An alternate filter such as Teflon is amenable to XRF and ion chemical analyses but is not amenable to analysis for carbon. To overcome these problems DRI constructed a medium-volume PM₁₀ sampler that is capable of collecting particulates on both Teflon and quartz fiber filters simultaneously. This paper describes the design of the DRI medium-volume PM₁₀ sampler, discusses a method for determining equivalence of two samplers, the results of applying the method to test the equivalence of the medium-volume sampler and a commerical high-volume sampler, and examines differences between PM₁₀ and TSP measurements in a southwestern desert.     

Prenatal diagnosis of a double heterozygote for two reciprocal translocations of familial origin

Two balanced reciprocal translocations were found in an amniotic fluid cell culture undertaken because of maternal age. One translocation had been inherited from each parent. Both translocations were traced through three generations of each family. The importance of banding techniques in diagnostic cytogenetics is stressed.     

Disappearing lung echogenicity in fetal bronchopulmonary malformations: A reassuring sign?

Congenital bronchopulmonary malformations detectable on prenatal ultrasound include cystic adenomatoid malformation (CAM), lobar sequestration, and upper airway atresia. We describe three fetuses with prenatally detected intrathoracic lesions in which the associated pulmonary hyperechogenicity disappeared before delivery. In the first case of pulmonary sequestration, the infant was asymptomatic after birth. However, in a case of CAM and another with laryngeal atresia, respiratory distress developed after delivery, despite recent scans showing apparently normal lung fields. This experience suggests that ultrasonic resolution of hyperechogenic lung lesions in utero does not necessarily indicate resolution of the underlying pathology.     

Amniotic fluid analysis in a fetus with laryngeal atresia

Complete laryngeal atresia is a rare congenital malformation that is known to cause hypertrophy of the fetal lung in utero. A fetus with laryngeal atresia was found to have markedly immature amniotic fluid lung maturity studies at term. Inappropriately low amniotic fluid lung maturity studies may be an important clue to the diagnosis of this condition.