Expositionsabschätzung: Human-Biomonitoring vs. Modellrechnungen

Exposure assessment represents an important and integral part of the assessment of health risks associated with the human exposure to toxic substances in soil and other environmental media. In recent times model calculations are widely used to assess the doses of toxic substances which have been incorporated into the human body via different routes of exposure. The present paper discusses the possibilities and limitations of such model calculations with regard to exposure and risk assessment. A critical point is that the results largely depend on the basic assumptions introduced into the model calculations. Moreover, the results refer to a more or less typical scenario of exposure, although they do not allow any conclusion with regard to individual exposure levels. In contrast, the use of biomarkers of exposure (human biological monitoring) represents a methodological approach to estimate individual exposure levels of subjects exposed to toxic substances in a given situation. In practice, the identification of persons at risk and the exclusion of individual health risks can only be based on human biological monitoring studies. Exposure assessment based on theoretical calculations and exposure assessment based on biomarkers of exposure and effects should be regarded as complementary approaches in exposure and risk assessment.     

Natal dispersal and philopatry in prairie voles (Microtus ochrogaster) in relation to population density,season, and natal social environment

Summary We used intensive livetrapping to examine natal dispersal and philopatry in prairie voles (Microtus ochrogaster). The majority of male (70.0%) and female prairie voles (75.1 %) remained at the natal nest until death. Those males and females that did disperse left home at about the same age (45–55 days) and moved similar distances (28–33 m). Dispersal was more common (1) from small natal groups than from large natal groups, (2) following disappearance of parents, (3) during the breeding period than during the nonbreeding period, and (4) at low population densities than at high densities. Dispersal was not associated with level of competition for mates within natal groups, and dispersers did not differ from nondispersers in body weight. Our data do not support competition for mates or resources as important factors influencing natal dispersal in prairie voles. The absence of sex differences in dispersal tendency or distance, and our fording that more than half of dispersers had become reproductive before leaving the natal nest, lead us to suggest that inbreeding avoidance is not a primary function of dispersal in this species. Dispersal was, however, more common when potential mates within the natal group were relatives than when they were nonrelatives. Although not tested here, if family members avoid mating with one another through patterns of mate choice, then some animals may leave home in search of mates. The precise benefits associated with philopatry in prairie voles remain to be identified. Correspondence to: B. McGuire at her present address     

The impact of differences in reliability data on the results of probabilistic safety analyses

The lack of plant-specific reliability data for probabilistic safety assessments is occasionally used for discrediting and doubting the validity of such analyses. On the other hand, analyses are often performed without even discussing the applicability of generic reliability data. In an attempt of clarification the impact of several sets of reliability data stemming from different sources on the explosion frequency of two processes with exothermal reactions (one of them is analyzed with plant-specific data) are quoted. As a further case study the reactor cooling system of one of the processes is analyzed. Additionally, a procedure using frequency and probability ranges is employed for comparison. The results show agreement within their respective uncertainty bounds; the identification of key components for safety is not hampered by data differences. The superiority of plant-specific data, which should of course be acquired, cannot be doubted. Nevertheless, improving the safety of a plant is possible using probabilistic safety analyses even with data which do not stem from the plant under investigation.     

Physiological tolerances across latitudes: thermal sensitivity of larval marine snails (Nucella spp.)

A critical step in understanding how temperature will affect biodiversity in coastal ecosystems is to gain insight into how the tolerances, and ultimately survival, of early life history stages will influence the distribution and abundance of adults. We assessed the thermal tolerance of encapsulated veliger-stage larvae of a common dogwhelk, Nucella ostrina, that occur in the rocky intertidal zone on the west coast of North America. Results showed that veligers collected from northern latitudes in Washington State were less tolerant of heat stress than those from central sites in California. For all sites, we found there to be a subtle difference between the temperatures at which veligers first began to die compared to when veligers reached 100% mortality. On a biogeographic scale, the LT₅₀ temperatures, a measure of larval sensitivity, for N. ostrina veligers displayed a strong latitudinal trend. These findings provide a conservative measurement of the upper thermal limits of encapsulated veligers while illustrating how these early life history stages could be physiologically compromised under future climate warming scenarios.