Scaling toxicity data across species

The response of various species to doses of chemicals can often give the impression that some (such as cattle in the case of molybdenum) are much more susceptible than others to these chemicals. These impressions usually rely on an underlying assumption that equivalent doses are based on mg of the chemical per kg body weight of the animal. That is, that doses scale as the first power of body weight. This assumption is more often wrong than right. When viewed in a more general way, where the scaling is proportional to a power of the body weight and the exponent determined empirically, it is often found that equivalent doses scale with an exponent in the range of 0.6 to 0.8. As a result, larger animals are indeed more susceptible to toxicity on a mg kg^–1 body weight basis, but this is not because of unique differences in the species, but only because of different body sizes. This method of scaling is called allometry or allometric scaling. An early version of this approach was based on body surface area where the exponent is 2/3. More recently, pharmacokinetics has revealed that the reason for the different response of larger animals is related to the slower metabolic and clearance rates for larger animals which give rise to larger biological half-lives for chemicals in the body and to higher tissue concentrations per given dose.     

Surfactive stabilization of multi-walled carbon nanotube dispersions with dissolved humic substances

Soil humic substances (HS) stabilize carbon nanotube (CNT) dispersions, a mechanism we hypothesized arose from the surfactive nature of HS. Experiments dispersing multi-walled CNT in solutions of dissolved Aldrich humic acid (HA) or water-extractable Catlin soil HS demonstrated enhanced stability at 150 and 300 mg L⁻¹ added Aldrich HA and Catlin HS, respectively, corresponding with decreased CNT mean particle diameter (MPD) and polydispersivity (PD) of 250 nm and 0.3 for Aldrich HA and 450 nm and 0.35 for Catlin HS. Analogous trends in MPD and PD were observed with addition of the surfactants Brij 35, Triton X-405, and SDS, corresponding to surfactant sorption maximum. NEXAFS characterization showed that Aldrich HA contained highly surfactive domains while Catlin soil possessed a mostly carbohydrate-based structure. This work demonstrates that the chemical structure of humic materials in natural waters is directly linked to their surfactive ability to disperse CNT released into the environment.     

A FACTOR ANALYSIS OF SOCIOECONOMIC CHANGE IN THE TENNESSEE RIVER WATERSHED1

ABSTRACT: Factor analysis is used to identify and summarize the socioeconomic changes occurring in the Tennessee River Watershed. A general factor analysis program is applied to a set of 25 socioeconomic variables hypothesized to represent many of the dimensions of regional socioeconomic change. The analysis identifies seven factors that underlie and explain socioeconomic change in the Tennessee River Watershed.     

ON PRECIPITATION SENSOR NETWORK DENSITIES FOR EVALUATING WINTERTIME OROGRAPHIC CLOUD SEEDING EXPERIMENTS1

Principal component analysis is used to investigate density requirements of wintertime orographic cloud seeding experiment precipitation sensor networks. Three passes in the vicinity of Climax, Colorado are studied. The eighteen or more evenly spaced precipitation sensors of each pass are almost completely described by three principal components. These three principal components appear to represent (i) mean precipitation, (ii) slope orientation to storm systems, and (iii) elevation. Evaluation of these principal components is implemented with two distribution-free tests, a proportionality test and the runs test. The results of this study suggest that the loss of experimental information caused by low density precipitation sensor networks may be of little consequence.     

Enzymes as river pollutants and the response of native epilithic extracellular-enzyme activity

Extracellular-enzyme activity was measured in three watercourses, in North East England, which received effluent from sewage-works. beta-D-glucosidase, leucine-aminopeptidase and phosphatase activities were markedly elevated in water downstream of outfalls. Despite subsequent downstream decrease, elevated activities persisted over several kilometres. Thus the effluents not only increased the quantity of organic matter in the rivers, they also increased enzymatic hydrolysis of polymeric compounds, thus increasing the supply of low-molecular-weight moieties available for microbial uptake and hence facilitating biopurification. Partitioning of river water, by 0.2 microm filtration, showed that free-enzyme activity was important as well as cell and particle-associated activity. Extracellular-enzyme activity was measured on stones from the bed of one watercourse. There was no evidence of end-product repression of native epilithic enzyme activity, even though enzyme activity in surrounding water was very high. Instead, beta-D-glucosidase and phosphatase activity increased on stones downstream of the outfall, and this was accompanied by an increase in the percentage of culturable epilithic bacteria capable of synthesizing extracellular beta-D-glucosidase and phosphatase.     

Colony genetic diversity affects task performance in the red ant Myrmica rubra

High relatedness and low genetic diversity among individuals in a group is generally considered crucial to the evolution of cooperative behaviour. However, in about a third of social insect species, intracolonial genetic diversity is increased because of derived polyandry (multiple mating by queens) and/or polygyny (multiple reproductive queens). Several studies have shown that increased intracolonial genetic diversity can enhance task performance in honey bees, but evidence of such effect in other social insects is still lacking. Why increased genetic diversity has evolved in some, but not all species, is a fundamental question in sociobiology. In this study, we investigated the effect of intracolonial genetic diversity on the task of nest migration, using the facultatively polyandrous and polygynous red ant Myrmica rubra. Genetic diversity significantly affected migration speed, but its effects were context dependent. Migration speed correlated positively with genetic diversity in one experiment in which migrations were into a known nest site, due to quicker transfer of brood into the new nest once consensus was reached. However, in a another experiment in which migration included scouting for new nest sites, migration speed correlated negatively with genetic diversity, due to slower discovery of new nest sites and slower transfer of brood into the new nest. Our results show for the first time that genetic diversity affects task performance in a social insect other than the honeybee, but that it can produce contrasting effects under different conditions.     

Geochemical investigations of metals release from submerged coal fly ash using extended elutriate tests

A storage pond dike failure occurred at the Tennessee Valley Authority Kingston Fossil Plant that resulted in the release of over 3.8 million cubic meters (5 million cubic yards) of fly ash. Approximately half of this material deposited in the main channel of the Emory River, 3.5 km upstream of the confluence of the Emory and Clinch Rivers, Tennessee, USA. Remediation efforts to date have focused on targeted removal of material from the channel through hydraulic dredging, as well as mechanical excavation in some areas. The agitation of the submerged fly ash during hydraulic dredging introduces river water into the fly ash material, which could alter the redox state of metals present in the fly ash and thereby change their sorption and mobility properties. A series of extended elutriate tests were used to determine the concentration and speciation of metals released from fly ash. Results indicated that arsenic and selenium species released from the fly ash materials during elutriate preparation were redox stable over the course of 10d, with dissolved arsenic being present as arsenate, and dissolved selenium being present as selenite. Concentrations of certain metals, such as arsenic, selenium, vanadium, and barium, increased in the elutriate waters over the 10d study, whereas manganese concentrations decreased, likely due to oxidation and precipitation reactions.     

Reproductive effort in Adélie penguins

Summary We estimated reproductive effort (energy expenditures for reproduction, as opposed to maintenance) in Adélie penguins breeding at Palmer Station, Antarctica. Data on body composition changes and metabolic rate were obtained using isotopic methods. Adelie breeding behavior consists of an initial courtship stage (during which both sexes fast), incubation, the guard stage (when chicks are 1 to 18–28 days old), and the creche stage (from the end of guarding until chicks are 28–45 days old). Both males and females lost considerable mass during the initial stages of the reproductive season, but males fasted longer and lost more mass. Mass losses of both sexes consisted of 66% depot fat and 34% lean tissue. Mass and body composition remained constant once birds resumed feeding. The metabolic expenditure for the foraging necessary to accumulate the mass lost while fasting — one component of reproductive effort —was about 63 MJ in males and 39 MJ in females. Field metabolic rates (FMR) were low during courtship and while incubating, increasing more than 2-fold when birds resumed foraging. Although mean FMR increased between incubation and the creche stage, differences between stages were small and not significant. We used FMR data and an energy balance model to estimate the cost of feeding chicks. Results suggest a maintenance FMR of about 2.7 × basal metabolism (BMR), increasing to 3.4–3.6 × BMR during the creche stage. The reproductive effort (as metabolic expenditures) associated with feeding chicks is 31 MJ (males) to 36 MJ (females). Cumulative reproductive effort is 94 MJ in males and 75 MJ in females, or 5.3–6.2% of the annual energy budget. The reproductive effort devoted to chick care does not appear to be constrained by physiological or time limitations. Instead, selection to reduce the risk of predation may prevent the evolution of increased parental care. Correspondence to: M.A. Chappell