The purpose of this study was to simultaneously evaluate several key factors which potentially affect the accumulation of hydrophobic pollutant compounds in sediment by benthic organisms. These factors were: (1) organic carbon content of the sediment; (2) equilibration time of the pollutant with the sediment; and (3) feeding strategies of the organism. [14C-U]2,4,5,2′,4′,5′-hexachlorobiphenyl (HCBP) was equilibrated with sediments from Narragansett Bay, RI containing either 4 or 2% total organic carbon for periods of either one or four weeks. Biological availability of the compound was assessed by following the kinetics of HCBP uptake into either the omnivorous deposit feeding polychaete Nephtys incisa or the deposit feeding bivalve Yoldia limatula exposed to bedded sediment. In an attempt to normalize bioaccumulation data for differences in the lipophilic reservoirs between sediment and organism, an apparent preference factor (APF) was calculated comparing body burdens normalized to % lipid with sediment concentrations normalized to % total organic carbon (TOC) APF = (HCBPs/$TOC)/(HCBPo/%lipid) For both organisms, APF reached a constant value within 20 days. Length of isotope incubation with sediment had no observable effect on either the rate of approach to a constant APF or the value of APF reached. Even after normalizing with the preference factor calculation, significant differences were still evident between bioaccumulation from the two sediment types and between bioaccumulation from the same sediment by Yoldia and Nephtys. These data indicate that in addition to the influence of sediment TOC and lipid content of the organism, intrinsic properties of sediment and biological properties of the organism influence the transfer and bioaccumulation of hydrophobic compounds.
In a 28 d microcosm study, we examined the effects of diesel-contaminated sediment on the sedimentary bacterial community of a Louisiana (USA) salt marsh that has been chronically exposed to petroleum hydrocarbons for decades Diesel contaminants in n1icrocosms as determined from polycyclic aromatic hydrocarbon (PAH) concentration ranged from 0.55 to 55 ppm (dry weight). Bacterial metabolism (incorporation of I4C-acetate and 3H-leucine) and bacterial abundance were not affected by diesel-contaminated sediment at any concentration. Bacterial degradation of I4C-phenanthrene, however, increased in direct proportion to the amount of diesel-contaminated sediment added. Ambient sediment also exhibited significant capacity to degrade PAH. The half life of phenanthrene (based on "'C-phenanthrene-degradation experiments) ranged from 137 d in ambient sediments to 4.5 d in sediment chronically exposed to high levels of diesel-contaminated sediments for 28 d. Two-and three-ring PAH, including naphthalenes, phenanthrenes, and dibenzothiophenes, constituted the bulk of PAH composition of diesel and were rapidly metabolized. Alkylated PAH were also readily metabolized. The rapid removal of PAH suggests that even if the marsh were exposed to chronically high levels of petroleum hydrocarbons, chemical evidence of the contaminants would not be detected in sediments. Collectively, these results are consistent with the hypothesis that the bacterial community in this salt marsh has adapted to chronic exposure to petroleum hydrocarbons.
Dysfunction in homeostatic mechanisms of cell death and proliferation are considered to be important in the pathogenesis of chemically induced neoplasia. p53 has been implicated in the regulation of cell death and proliferation. To determine whether expression of apoptosis, proliferating cell nuclear antigen (PCNA), and p53 differ between an alkylating agent and a polycyclic aromatic hydrocarbon, host response was measured through sequential immunohistochemical detection of apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method), PCNA PC-10, and p53 (PAb 240) in livers of the fish Fundulus grandis. Nine hundred fish were randomly assigned to 3 groups of 300 fish each and kept in separate aquarium tanks. One group of fish was exposed to 6.7 μM N -methyl-N' -nitro-N -nitrosoguanidine (MNNG), 1 group was exposed to 6.9 mM 2-aminofluorene (2-AF), and the remaining group served as a control. A significant decrease (p = 0.005) in the level of apoptosis and a significant increase (p < 0.0001) in the level of p53 were found on experimental day 180 in the livers of MNNG-exposed fish. PCNA was significantly increased (p < 0.005) by day 9 of the experiment in both MNNG and 2-AF fish when compared with controls, but no significant differences existed between the 2 groups of treated fish. Response of fish liver cells to MNNG-mediated and 2-AF-mediated injury differs, at least initially, in the expression of p53, inhibition of apoptosis, and increased net cell proliferation. Concurrent use of a marker for cell death with a marker of proliferation greatly enhances the assessment of the effect of these compounds on liver cells.
Oil drilling operations generate very large volumes of produced waters which contain a complex mixture of sub-surface water and solid and liquid geological materials, including crude oil, drilling fluids, and treatment chemicals. In coastal regions, these produced waters are discharged into fresh or brackish marshes or wetlands which also serve as the spawning sites for a wide variety of economically important species of fish and shellfish. Recently, concern has focused on potential impacts of produced waters upon these productive and sensitive ecosystems. In the present study, we report the results of investigations which characterize the chemical contaminants present in produced waters and surficial sediments collected at two sites in coastal Louisiana. Trace organic analyses of the produced waters revealed a complex and variable mixture of normal-, alkyl-, and heterocyclic polynuclear aromatic hydrocarbons. Examination of surficial and sub-surface sediments demonstrate that extensive areal distribution of the produced water hydrocarbons has occurred through time. Embryonic stage genotoxicity bioassays of the produced waters indicate that the polycyclic aromatic hydrocarbons being discharged in these coastal waters cause increased mutational frequencies in Cyprinodon variegatus. Since the observation of chromosomal aberrations is usually rare in the cells of the organism and since cell replication and differentiation are maximal in the early developmental stages of these and other species of aquatic organisms, the results suggest that the potential exists for adverse effects of these discharges on estuarine productivity. Further study of the impacts of produced waters in this and other species is indicated.
It is widely believed that most chemical carcinogens act by binding to cellular genetic material and causing somatic mutations. Chemical modification of DNA (e.g., the formation of DNA adducts) is the first in a series of stages that lead to mutation, cell transformation, and tumor development. Sensitive methods for detection of DNA adducts are essential for mechanistic studies of mutagenesis and carcinogenesis and for biomonitoring of populations at risk for environmentally caused cancer. DNA adducts may be detected with such methods as 32Ppostlabeling, immunoassays, HPLC with fluorescence detection, and gas chromatography/mass spectrometry, with varying degrees of sensitivity and structural specificity. Alkylation at the N-7 position of guanine is a preferential site of attack for most alkylating agents, but may be of little biological consequence, while adduct formation at the O6 position of guanine (less common) is most highly correlated with carcinogenesis. We have examined the suitability of western mosquitofish (Gambusia affinis) as a native sentinel species for monitoring environmental exposures to mutagens and carcinogens. Mosquitofish are a native species to the U.S. and are also widely distributed in warm waters throughout the world. These fish are ideal for monitoring local exposures because they are non-migratory and are found in a wide variety of habitats. In the laboratory, they are easily cultured using techniques developed for other small fish species and appear resistant to infectious diseases. Thus, methods may be directly assessed under controlled conditions before being applied to field situations. In these studies, mosquitofish were exposed to a model alkylating agent, methylazoxymethanol acetate, at 10 ppm in the ambient water for 2 h. Fish were then transferred to clean water and held for up to 72 h. Livers were excised, pooled for 5 fish, and DNA was extracted and prepared for analysis. Liver DNA extracts were assessed for levels of N-7 and O6-methylguanine by isotope dilution GC/mass spectrometry, using deuterated analogs of methylguanine adducts as standards. Detection limits for the assay were approximately 1.6 femtomoles of adduct per mg DNA (about 1 adduct per 2 million bases). Approximately 55–185 pg (330–1100 femtomoles) O6 -methylguanine per mg DNA were measured in exposed fish in the first 72 h after exposure. These lesions were correlated with a 33% liver tumor incidence after 25 weeks in parallel experiments.
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