No abstract

No abstract

No abstract

The purpose of this study was to determine the effects of perchlorate on thyroid function in mosquitofish. Adult mosquitofish were exposed to 0, 0.1, 1, 10, 100, and 1000 mg/L sodium perchlorate for 2, 10, and 30 d. Whole body thyroxin (T4) content and histological assessment of thyroid follicles (e.g., follicular epithelial height, hyperplasia, hypertrophy, and colloid depletion) were used to gauge alterations in thyroid function. Follicular epithelial cell height, hyperplasia, and hypertrophy increased with increasing perchlorate concentration, especially in fish exposed for 30 d, and these effects were statistically significantly different from control at concentrations as low as 0.1 mg/L (nominal concentration). The percent occurrence of follicles with depleted colloid decreased with increasing perchlorate concentration, which is contrary to what is expected with thyroid inhibition. There also was a decrease in whole body T4 concentration in fish exposed to perchlorate for 30 d, but clear dose-response relationships were less evident for whole body T4 than for histopathological endpoints. In conclusion, thyroid histopathology provides a sensitive biomarker for thyroid endocrine disruption at environmentally relevant concentrations of sodium perchlorate, and whole body T4 is a less sensitive indicator of perchlorate exposure than is histopathology.

A polynya that forms each winter south of St. Lawrence Island in the Bering Sea is located near very high standing stocks of macrobenthic invertebrates on this Arctic continental shelf. Sampling during or just after the ice melt in 1990, 1993, and 1994 revealed water-column, sediment particle and chemical distributions that were consistent with a high flux of organic materials to the sediments during the ice retreat. In contrast, lower phytoplankton biomass observed in late summer and fall of 1993, 1998, and 1999 was associated with seasonal declines in sedimentation indicators such as chlorophyll a in the water column and deposited on the surface sediments, lower occurrences of an atmospherically derived radionuclide beryllium-7 (7 Be) in surface sediments, and lower sediment oxygen demand. Moreover, observations under late-winter conditions in April 1999 did not support a direct, continuous linkage between water-column production when the winter polynya is active and the very high benthic biomass and productivity observed on this shallow (30 to 60 m) shelf. For example, deposition of recent water-column production to the sediments in April was significantly lower than that during and just after the ice retreat in May and June. This lower rate of deposition in April was inferred from proxy indicators including photosynthetically-competent chlorophyll extractable from surface sediments, the presence of 7 Be in surface sediments, and sediment oxygen demand. Despite high nutrient concentrations, water-column chlorophyll a concentrations were also uniformly lower (0.5 to 2 mg m-3) in April than in May and June. Measurements of the underwater light and ultraviolet radiation field and analysis of DNA damage to dosimeters indicated that the low chlorophyll a biomass is probably not influenced by UV radiation in late winter and early spring. The stable carbon isotope composition of organic carbon in surface sediments suggests that open-water production in the polynya, relative to the adjacent production of sea-ice algae, is not large enough to influence the isotopic composition of organic materials in surface sediments near the polynya.

Aflatoxin B1 (AFB1) and T-2 toxin (T-2) are important food-borne mycotoxins that have been implicated in human health and as potential biochemical weapons threats. In this study the acute and combinative toxicity of AFB1 and T-2 were tested in F-344 rats, mosquitofish (Gambusia affinis), immortalized human hepatoma cells (HepG2) and human bronchial epithelial cells (BEAS-2B). Preliminary experiments were conducted in order to assess the acute toxicity and to obtain LD50, LC50 and IC50 values for individual toxins in each model, respectively. This was followed by testing combinations of AFB1 and T-2 to obtain LD50, LC50 and IC50 values for the combination in each model. All models demonstrated a significant dose response in the observed parameters to treatment. The potency of the mixture was gauged through the determination of the interaction index metric. The results of this study demonstrate that these two toxins interacted to produce alterations in the toxic responses generally classifiable as additive; however, a synergistic interaction was noted in the case of BEAS-2B. It can be gathered that this combination may pose a significant threat to public health and further research needs to be completed addressing alterations in metabolism and detoxification that may influence the toxic manifestations in combination.

We examined effects of radionuclide exposure at two atomic blast sites on kangaroo rats (Dipodomys merriami) at the Nevada Test Site, Nevada, USA, using genotoxicity and population genetic analyses. We assessed chromosome damage by micronucleus and flow cytometric assays and genetic variation by randomly amplified polymorphic DNA (RAPD) and mitochondrial DNA (mtDNA) analyses. The RAPD analysis showed no population structure, but mtDNA exhibited differentiation among and within populations. Genotoxicity effects were not observed when all individuals were analyzed. However, individuals with mtDNA haplotypes unique to the contaminated sites had greater chromosomal damage than contaminated-site individuals with haplotypes shared with reference sites. When interpopulation comparisons used individuals with unique haplotypes, one contaminated site had greater levels of chromosome damage than one or both of the reference sites. We hypothesize that shared-haplotype individuals are potential migrants and that unique-haplotye individuals are potential long-term residents. A parsimony approach was used to estimate the minimum number of migration events necessary to explain the haplotype distributions on a phylogenetic tree. The observed predominance of migration events into the contaminated sites supported our migration hypothesis. We conclude the atomic blast sites are ecological sinks and that immigration masks the genotoxic effects of radiation on the resident populations.

To determine effects of pulp mill effluent on population genetic structure, redbreast sunfish (Lepomis auritus) were collected from several sites along the Pigeon River, NC, as well as from reference sites. Previous studies found effects on molecular, biochemical, physiological, population, and community level endpoints in these populations. The population genetic structure of these fish was determined using the randomly amplified polymorphic DNA (RAPD) technique. The level of genetic diversity was higher in the Pigeon River populations than in the reference populations. Genetic distances among populations could not be explained by drainage patterns and may have been altered by contaminant exposure. Phylogeographic analysis, maximum likelihood analysis, and assignment tests suggested that there were fewer emigrants and more immigrants in the contaminated sites than in the reference sites, suggesting that the contaminated sites may harbor "sinklike" populations. Finally, a "terminal branch amplitype" analysis (neighbor-joining and minimum-spanning trees) and maximum likelihood analysis indicated that there may be an elevated mutation rate in the polluted sites. Thus, the genetic diversity (within and among populations) in the Pigeon River populations may have been affected by altered gene flow and mutational processes as a result of pulp mill effluent discharge.