Defining Acceptable Levels for Ecological Indicators: An Approach for Considering Social Values

Ecological indicators can facilitate an adaptive management approach, but only if acceptable levels for those indicators have been defined so that the data collected can be interpreted. Because acceptable levels are an expression of the desired state of the ecosystem, the process of establishing acceptable levels should incorporate not just ecological understanding but also societal values. The goal of this research was to explore an approach for defining acceptable levels of ecological indicators that explicitly considers social perspectives and values. We used a set of eight indicators that were related to issues of concern in the Lake Champlain Basin. Our approach was based on normative theory. Using a stakeholder survey, we measured respondent normative evaluations of varying levels of our indicators. Aggregated social norm curves were used to determine the level at which indicator values shifted from acceptable to unacceptable conditions. For seven of the eight indicators, clear preferences were interpretable from these norm curves. For example, closures of public beaches because of bacterial contamination and days of intense algae bloom went from acceptable to unacceptable at 7–10 days in a summer season. Survey respondents also indicated that the number of fish caught from Lake Champlain that could be safely consumed each month was unacceptably low and the number of streams draining into the lake that were impaired by storm water was unacceptably high. If indicators that translate ecological conditions into social consequences are carefully selected, we believe the normative approach has considerable merit for defining acceptable levels of valued ecological system components.     

甲苯二异氰酸酯(TDI)致癌性的综合评估

甲苯二异氰酸酯(TDI)被数家机构分类为可能的人类致癌物,其主要依据为动物实验发现对啮齿动物经灌胃暴露TDI后肿瘤发生率升高。基于研究结果的可靠性以及一致性,综合评估了现有研究数据是否支持这一分类。结果显示现有的流行病学数据不足以有力证明TDI为人类致癌物。动物实验研究表明,吸入接触TDI并不导致肿瘤发生。经灌胃暴露后观察到的肿瘤很可能是由于TDI转化为已知的啮齿动物致癌物甲苯二胺(TDA)所致。在TDI吸入暴露的体内实验中,当由TDI转化生成的TDA不能达到具有显著生物学效应的浓度时,TDI对啮齿动物或人类都没有遗传毒性。由于哺乳动物在生理性接触条件下TDI不能转变成TDA,所以对人类而言,TDI接触与致癌效应之间无直接的显著因果关系。因此虽然在如灌胃等非生理暴露的条件下,TDI可能的人类致癌物的分类是正确的,但本文对其致癌研究数据的合理评估和正确理解有助于将产品监管力度集中于与职业暴露更相关的有害健康效应上。     

Target and nontarget discrimination of herbicides applied to vegetation in a power-line corridor

We tested two cutting regimens (cut/spray and cut/delay spray) and four radiarc-applied herbicides (Garlon + Tordon, Accord, Accord + Escort, and Krenite) in an Ohio power-line corridor to determine which management combination best eliminated target species (i.e., trees) and preserved nontarget species (i.e., low shrubs, vines, perennial herbs, and grasses). When spraying was delayed after cutting, the herbicide with the least impact on nontarget species (Krenite) also was least efficient at killing target trees. Spraying soon after cutting improved tree-killing efficiency of several herbicides, but it also increased the negative impact on nontarget species. The herbicide with the most consistent tree-killing ability (Accord + Escort) had the most impact on nontarget species. Because none of the herbicide/cutting treatments performed ideally, resource managers must decide the acceptable impact on nontarget species when considering herbicide use. Future success of herbicides as part of an integrated succession management approach requires more selective application methods and formulations so that target effects can be maximized and nontarget effects can be minimized.     

Do newborn domestic rabbits Oryctolagus cuniculus compete for thermally advantageous positions in the litter huddle?

Competition among mammalian siblings for scarce resources can be severe. Whereas research to date has focused on competition for the mother’s milk, the young of many (particularly altricial) species might also be expected to compete for thermally favorable positions within the nest, den, or litter huddle. We investigated this in newborn pups of the European rabbit Oryctolagus cuniculus, a species in which the altricial young are not brooded by the mother, and in which competition for milk is severe. In eight unculled litters (N = 86 pups) of a domestic chinchilla strain, we calculated huddling indexes for individual pups on postnatal days 2–5 as a measure of the degree of insulation they received from littermates. Pups maintained almost constant physical contact with the litter huddle. They performed brief but frequent rooting and climbing behaviors, which usually improved their huddling index, interspersed with longer periods of quiescence during which their huddling index declined. As expected, we found a significant positive relation between pups’ mean huddling index and body temperature. Unexpectedly, however, we did not find a relation between huddling index and pups’ birth weight, survival, milk intake, or efficiency of converting milk to body mass. We conclude that rather than competing for thermally advantageous positions within the huddle newborn rabbits share out thermally advantageous positions as they move in a continual dynamic flow through it. Thus, in newborn rabbits, competition for the mother’s milk exists alongside mutual “cooperative” benefits of littermate presence. This contribution is part of the special issue “Sibling competition and cooperation in mammals” (guest editors: Robyn Hudson and Fritz Trillmich).     

Effect of temperature and humidity on formaldehyde emissions in temporary housing units

The effect of temperature and humidity on formaldehyde emissions from samples collected from temporary housing units (THUs) was studied. The THUs were supplied by the U.S. Federal Emergency Management Administration (FEMA) to families that lost their homes in Louisiana and Mississippi during the Hurricane Katrina and Rita disasters. On the basis of a previous study, four of the composite wood surface materials that dominated contributions to indoor formaldehyde were selected to analyze the effects of temperature and humidity on the emission factors. Humidity equilibration experiments were carried out on two of the samples to determine how long the samples take to equilibrate with the surrounding environmental conditions. Small chamber experiments were then conducted to measure emission factors for the four surface materials at various temperature and humidity conditions. The samples were analyzed for formaldehyde via high-performance liquid chromatography. The experiments showed that increases in temperature or humidity contributed to an increase in emission factors. A linear regression model was built using the natural log of the percent relative humidity (RH) and inverse of temperature (in K) as independent variables and the natural log of emission factors as the dependent variable. The coefficients for the inverse of temperature and log RH with log emission factor were found to be statistically significant for all of the samples at the 95% confidence level. This study should assist in retrospectively estimating indoor formaldehyde exposure of occupants of THUs.     

Ecological and Toxicological Effects of Exposure to an Acidic, Radioactive Tailings Storage

The persistence of an island of remnant vegetation within a tailings retention system provided an opportunity to conduct a pilot study to develop hypothesis concerning the impacts of acid spray and radiation on arid zone flora and fauna. Ecological changes were investigated by comparing species abundance and condition on both the study island and remote control areas. Hopbush (Dodonaea viscosa), geckos and a common ant species, Iridomyrmex rufoniger sp. B were abundant in control regions but absent from the study region, whereas densities of colonising plant species, Helea beetles and scorpions were unusually high at the impacted site. These disparities are probably attributable to acid spray at the impacted site and hence are potentially useful bioindicators of these impacts. Dragon and skink populations were apparently unaffected by the polluted ecosystem, although Ctenophorus nuchalis proved to be a significant bioaccumulator of radionuclides. Bioaccumulation of the radionuclides, ²³⁸U, ²³⁰Th, ²¹⁰Pb and particularly ²¹⁰Po were significantly greater than that reported elsewhere in the literature. Further radionuclide monitoring of herbivorous dragon species, possibly concentrating upon ²¹⁰Po levels, was the suggested outcome of this pilot study.