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Biomedical subjects

D L Stuart

Publications and source records attributed to D L Stuart.

5 recordsLinked to original sources
PubMed2003

Comparative bioavailability of selenium to aquatic organisms after biological treatment of agricultural drainage water.

Selenium (Se) is naturally abundant in the soils of the western San Joaquin Valley, California, USA. Intense agricultural activity in this region requires irrigation which leaches Se into surface waters draining to the San Joaquin River. Se water contamination and subsequent accumulation in wildlife is a serious problem in the Central Valley of California, and the subject of increasingly intensive regulatory action. Algal-bacterial selenium reduction (ABSR) is a potential new treatment approach to reduce Se in agricultural drainage, and an ABSR demonstration facility was examined with respect to its Se removal efficiency and effect on Se bioavailability and bioaccumulation. Water samples were taken to study treatment effects on Se speciation. Invertebrate tissue Se concentrations in the ABSR ponds were monitored for 2 years. Laboratory-based algal bioaccumulation tests and in situ microcosms with a variety of invertebrates were also used to address differences in Se bioavailability before and after ABSR treatment. The ABSR system removed about 80% of the total influent Se; however, microbial and algal activity produced selenite and organic Se, the combined concentration of which increased 8-fold during treatment. As a result of the greater bioavailability of selenite and organic Se, relative to the selenate of the influent, treatment contributed to greater Se concentrations in effluent-exposed organisms. ABSR-treated water produced Se concentrations in biota 2-4 times greater than organisms exposed to untreated water. The bioavailability of Se in the treated water was 2-10 times greater than Se in the influent. The shift to more bioavailable Se forms due to biological treatment is inherent in system design, and makes it difficult to weigh the ecological benefits of a reduction in total Se loadings from a regional perspective against the greater toxicological risk to biota in the vicinity of the effluent.

Animals↗
PubMed2001

Valepotriates and valerenic acids in commercial preparations of valerian available in Australia.

Thirty-one commercial valerian preparations available in Australia, including teas, tablets, capsules and liquids, were analysed by HPLC for valepotriates, valerenic acid and valerenic acid derivatives. The concentration of valerenic acid and its derivatives ranged from < 0.01 to 6.32 mg/g of product. Powder capsules, on average, contained the highest concentration of valerenic acids (2.46 mg/g) and liquids the lowest concentration (0.47 mg/ml). The mean concentration of valerenic acid in the five products standardized against valerenic acid (3.56 mg/g) was significantly higher than in the 26 non-standardized products (0.89 mg/g). There was a significant relationship between valerenic acids content and added valerian root for the standardized products but not for the non-standardised products. Valepotriates were found at low levels (< 1.0 mg/g) in some teas but were not detected in any of the finished products.

Australia↗
PubMed2000

Tick histamine-binding proteins: lipocalins with a second binding cavity.

Tick histamine-binding proteins (HBPs) are lipocalins with two binding pockets. One of these binds histamine with a high affinity and is found at the position expected from other lipocalins, adjacent to the omega-loop at the open-end of the beta-barrel. A second binding cavity, which is a low-affinity site for histamine in one of the HBPs, is located at the end of the barrel that is closed off in other lipocalins. In order to create the second site, the 'closed-end' region has undergone a major reconstruction. Typical lipocalin characteristics, such as the 3(10) helix and a structural cluster of highly conserved residues, have been lost, while an alpha-helix now shields the cavity from the exterior. The prominence of acidic residues in the binding pockets is another distinctive characteristic of HBPs. Whereas most lipocalins have highly hydrophobic binding cavities designed to bind lipophilic compounds, HBPs have evolved to trap cationic, hydrophilic molecules.

Amino Acid Sequence↗
PubMed1993

The human ecology of tornadoes.

This paper offers an empirical test of the impact of human ecological patterns and other known correlates on tornado occurrence. It uses the National Severe Storms Forecast Center's information on tornadoes from 1950 through 1990 and employs ecological data from the U.S. Bureau of the Census and the Environmental Protection Agency. The results show that metropolitan and other urban counties have higher odds of tornado occurrence than rural counties, and that the probability of occurrence of tornadoes increases with increases in the number of previous tornadoes. The paper assesses the meaning of this finding for demographers, atmospheric scientists, engineers, and disaster managers.

Disasters↗