Effects of field exposure to diazinon on small mammals inhabiting a semienclosed prairie grassland ecosystem. I. Ecological and reproductive effects.

The widespread use of cholinesterase-inhibiting pesticides in the environment presents increasing concerns about their effects on human, wildlife, and ecosystem health. As a group, these pesticides are generally highly toxic and have great potential for negatively affecting nontarget organisms. Small mammals have proven to be ideal biomonitors of environmental contaminants, and were used here to test for possible effects of a widely used cholinesterase-inhibiting insecticide, diazinon, in a natural field setting. Using 12 0.1-ha terrestrial mesocosms, we examined the effects of low-level diazinon exposure on the small mammal communities inhabiting semienclosed grassland ecosystems. Our primary objective was to test the hypothesis that diazinon, applied at two different recommended label application rates, would not cause any observable adverse ecological or reproductive effects on small mammal populations and communities. Experimental small mammal communities consisting of Sigmodon hispidus, Microtus ochrogaster, Reithrodontomys fulvescens, and Mus musculus were stocked at natural densities and sex ratios inside empty mesocosms. Diazinon 4E was applied at two different maximum recommended label application rates, 0.56 kg a.i./ha (1x) and 4.5 kg a.i./ha (8x), and controls remained unsprayed, with four enclosures (replicates) per treatment. Two 30-d trials were run during peak rodent breeding seasons and enclosures were sampled on days 2, 16, and 30 of each trial. Recovery of small mammals was not significantly different among treatments, although fewer animals were recovered from the diazinon-exposed enclosures in both trials. Analysis of trapping data suggested that the normally strong competitive relationship between Sigmodon and Microtus may be altered by the pesticide, favoring Microtus in the diazinon-exposed enclosures. Incidence of reproductive condition was found to be reduced 20 to 80% and 33 to 100% in diazinon-exposed males and females, respectively. Reproductive productivity, including percentage of pregnant females and of females giving birth, was significantly reduced in diazinon-exposed animals. Percentage of pregnant females ranged from 13.6 to 43.5% in diazinon-exposed animals compared to 40 to 80% for control animals, and percentage of females giving birth ranged from 0 to 17% in diazinon-exposed animals compared to 22 to 50% for control animals. Generally, the effects found in this study suggest that diazinon was relatively persistent in the sprayed enclosures and that oral routes of exposure (consumption of dead and dying arthropods, grooming) may have been important. Ecological relationships and reproduction in both herbivorous and omnivorous mammals were negatively impacted by diazinon exposure. Overall, ecological relationships in the enclosed prairie grassland ecosystem were disrupted by diazinon, probably through a combination of sublethal effects, particularly reproductive effects, impacting individuals and their populations. This suggests that negative impacts on populations and community structure and function may persist longer than diazinon persists in the environment.

Classification of grossly detectable abnormalities and conditions seen at postmortem in Canadian poultry abattoirs according to a hazard identification decision tree.

This study was designed to review all grossly detectable abnormalities and conditions (GDACs) encountered in poultry in Canadian abattoirs to determine which have potential to cause adverse health effects for the consumer. Review of the literature and consultation with scientists in the field of microbiology, epidemiology, poultry pathology, chemistry, and meat inspection served to generate an inventory of GDACs, and a decision tree containing algorithms was developed to identify GDACs potentially representing a health hazard to consumers. Through the use of the decision tree, GDACs were classified into different categories with regard to the risk they represent to humans. A number of GDACs were identified as being of potential concern from a food safety perspective, namely Erysipelas, fowl cholera, Campylobacteriosis, clostridial diseases, hepatitis/enteritis associated with Helicobacter, Listeriosis, Salmonella infections (nontyphoid infections, Salmonella arizonae, pullorum disease, and fowl typhoid), Staphylococcosis, and Toxoplasmosis. Further characterization--i.e., hazard characterization, exposure assessment, and risk characterization--is required to quantify or better characterize the probability that products derived from affected carcasses may affect the consumer as well as the resulting consequences. Risk assessment is a dynamic process. Results presented in this paper are based on available information and expert opinion. As new information is obtained, the inventory of GDACs and their classification may be modified.

Mesocosms in ecotoxicology (1): Outdoor aquatic systems.

Mesocosms have been used in aquatic ecotoxicology for approximately 20 years and were sometimes claimed to be essential tools, especially for regulatory purposes. The term aquatic mesocosm currently describes indoor and outdoor artificial streams or experimental ponds and enclosures. The use of mesocosms refines the classical methods of ecotoxicological risk assessment because mesocosms provide conditions for a better understanding of environmentally relevant effects of chemicals. They make it possible to assess effects of contaminants by looking at the parts (individuals, populations, communities) and the whole (ecosystems) simultaneously. Ecotoxicological investigations in mesocosms will not entirely replace the use of laboratory animals. However, they allow tests to be performed on species that are not of major societal concern, but which play key roles in the structure and function of ecosystems. In this respect, mesocosms allow nondestructive measurements of integrated endpoints. They also appear as potent tools to predict changes at the highest levels of organization (population, community, and ecosystem) from measurements of individual endpoints. However, after a period of extensive use, regulatory studies using large-scale mesocosms were more or less abandoned at the beginning of the 1990s, mainly because their cost-effectiveness was questionable. This review covers key features of outdoor aquatic mesocosms that can be critical for their use in environmental risk assessment of chemicals and emphasizes the optimization of their use for such purpose. The originality of mesocosms is mainly based on the combination of ecological realism, achieved by introduction of the basic components of natural ecosystems, and facilitated access to a number of physicochemical, biological, and toxicological parameters that can be controlled to some extent. This characteristic determines various features of the systems such as the minimal size required, initial physicochemical and biological composition, or choice of model species for ecotoxicological investigations. Ecological maturity of mesocosms affects the degree of variability of both physicochemical and biological parameters used to investigate the impact of contaminants. Adequate time is required to establish a number of interacting functional groups. The choice of appropriate time scales must be considered in the selection of both study duration and sampling frequency. Whatever the system used, duration of experiments should be sufficient to identify both direct and indirect effects on populations and communities. The choice of the experimental design should be based on the objectives of the study rather than on theoretical considerations. In addition to classical parametric statistical methods, nonparametric approaches and multivariate analysis may significantly improve data processing. Realism, representativity, and replicability of mesocosms are critical for evaluating their usefulness in both risk and impact assessment procedures. Each natural ecosystem is unique because its structure and function mainly depend on local factors. Therefore, there is a conceptual opposition between realism and replicability when applied to mesocosms. Considering the objectives of most mesocosm studies, replicability should be preferred to realism. Replicability may be achieved, in part, by a relative simplification of the systems. Reconstituted systems do not need to exactly simulate natural conditions at all levels, but key features at both structural and functional levels should be preserved as they ensure ecological representativity. Reliability of information on ecotoxicological effects of chemicals tested in aquatic mesocosms closely depends on the representativity of biological processes or structures that are likely to be affected. Extrapolation from small experimental systems to the real world seems generally more problematic than the use of larger systems in which more complex interacti

Superficial siderosis of the central nervous system: a late complication of cerebellar tumors.

OBJECTIVE: To describe the clinical and radiologic features of superficial siderosis of the CNS after treatment of a cerebellar tumor. METHODS: Clinical assessment and MRI in four patients with superficial siderosis were performed. RESULTS: Four patients with superficial siderosis had been treated for a primary cerebellar tumor (astrocytoma in three patients, medulloblastoma in one patient) during childhood. All patients were treated with surgery and three received radiotherapy. Slowly progressive bilateral sensorineural hearing loss, gait ataxia, and limb ataxia appeared 8 to 22 years after diagnosis of the cerebellar tumor. Other clinical features were mild cognitive impairment, dysarthria, nystagmus, optic neuropathy, anosmia, and upper motor neuron signs. The CSF contained erythrocytes and increased protein. MRI with fast spin-echo T2-weighted and gradient-echo T2* sequences showed a hypointense rim of iron coating the surface of the cerebellum and brainstem. Twenty-one other patients who had survived more than 5 years after treatment of a primary cerebellar tumor did not have symptoms or signs suggestive of superficial siderosis. CONCLUSIONS: Superficial siderosis is an uncommon late complication of the treatment of a childhood cerebellar tumor, but it is probably underrecognized. The diagnosis should be suspected in patients who present with slowly progressive sensorineural hearing loss and ataxia many years after eradication of a childhood cerebellar tumor.

13th Meeting of the Scientific Group on Methodologies for the Safety Evaluation of Chemicals (SGOMSEC): alternative testing methodologies for ecotoxicity.

There is growing public pressure to minimize the use of vertebrates in ecotoxicity testing; therefore, effective alternatives to toxicity tests causing suffering are being sought. This report discusses alternatives and differs in some respects from the reports of the other three groups because the primary concern is with harmful effects of chemicals at the level of population and above rather than with harmful effects upon individuals. It is concluded that progress toward the objective of minimizing testing that causes suffering would be served by the following initiatives--a clearer definition of goals and strategies when undertaking testing procedures; development of alternative assays, including in vitro test systems, that are based on new technology; development of nondestructive assays for vertebrates (e.g., biomarkers) that do not cause suffering; selection of most appropriate species, strains, and developmental stages for testing procedures (but no additional species for basic testing); better integrated and more flexible testing procedures incorporating biomarker responses, ecophysiological concepts, and ecological end points (progress in this direction depends upon expert judgment). In general, testing procedures could be made more realistic, taking into account problems with mixtures, and with volatile or insoluble chemicals.

Chemical cues from families delay puberty in male California voles.

The role of chemical cues in the delay of puberty in male California voles (Microtus californicus) was investigated. Males that were raised from weaning in bedding from their families were delayed in attainment of adult androgen levels and seminal vesicle weights compared to males raised in clean bedding. In a second experiment, the source of the suppressive cues was examined by rearing males in bedding from unrelated adult males, their fathers, or their mothers. Males reared with bedding from their mothers showed delayed maturation of both androgen levels and seminal vesicle weights, whereas males exposed to bedding from unrelated males were not delayed. Males exposed to bedding from their fathers showed intermediate androgen levels but large seminal vesicles. Thus, chemical cues from the family, particularly the mother, suppress reproductive development in male California voles. These results are discussed in the context of the puberty delay which occurs in natural populations of this species; it is suggested that puberty delay is an adaptive strategy that may be employed by young voles in times of high density and limited resources.