Chemical pollutants in relation to diseases in fish

Novel sensor technologies towards environmental health monitoring in urban environments: a case study in the Niger Delta (Nigeria)

The Niger Delta (Nigeria) is an exemplar of a legacy of environmental pollution. Limited knowledge on spatial and temporal pollutant distributions in the region highlights the need for biomonitoring approaches to study impacts on sentinel organisms. This study evaluated whether infrared (IR) spectroscopy and multivariate analysis could detect alterations in biomolecules in samples in differing exposure scenarios, i.e., spatial and temporal using African catfish (Heterobranchus bidorsalis) or water spinach (Ipomea aquatica). Significant spectral differences between tissues isolated from African catfish based on site or season were observed; in a region where fish appeared not to be present, water spinach was used as a surrogate sentinel organism. Using one-way ANOVA, the spectral categories were significant (P < 0.0001). The applicability of IR spectroscopy to detect subtle changes in target biological molecules within sentinel organisms along with its low-cost yet high-throughput potential suggests that biospectroscopy permits real-time evaluation of environmental exposure effects.

Fish bioaccumulation and biomarkers in environmental risk assessment: a review

In this review, a wide array of bioaccumulation markers and biomarkers, used to demonstrate exposure to and effects of environmental contaminants, has been discussed in relation to their feasibility in environmental risk assessment (ERA). Fish bioaccumulation markers may be applied in order to elucidate the aquatic behavior of environmental contaminants, as bioconcentrators to identify certain substances with low water levels and to assess exposure of aquatic organisms. Since it is virtually impossible to predict the fate of xenobiotic substances with simple partitioning models, the complexity of bioaccumulation should be considered, including toxicokinetics, metabolism, biota-sediment accumulation factors (BSAFs), organ-specific bioaccumulation and bound residues. Since it remains hard to accurately predict bioaccumulation in fish, even with highly sophisticated models, analyses of tissue levels are required. The most promising fish bioaccumulation markers are body burdens of persistent organic pollutants, like PCBs and DDTs. Since PCDD and PCDF levels in fish tissues are very low as compared with the sediment levels, their value as bioaccumulation markers remains questionable. Easily biodegradable compounds, such as PAHs and chlorinated phenols, do not tend to accumulate in fish tissues in quantities that reflect the exposure. Semipermeable membrane devices (SPMDs) have been successfully used to mimic bioaccumulation of hydrophobic organic substances in aquatic organisms. In order to assess exposure to or effects of environmental pollutants on aquatic ecosystems, the following suite of fish biomarkers may be examined: biotransformation enzymes (phase I and II), oxidative stress parameters, biotransformation products, stress proteins, metallothioneins (MTs), MXR proteins, hematological parameters, immunological parameters, reproductive and endocrine parameters, genotoxic parameters, neuromuscular parameters, physiological, histological and morphological parameters. All fish biomarkers are evaluated for their potential use in ERA programs, based upon six criteria that have been proposed in the present paper. This evaluation demonstrates that phase I enzymes (e.g. hepatic EROD and CYP1A), biotransformation products (e.g. biliary PAH metabolites), reproductive parameters (e.g. plasma VTG) and genotoxic parameters (e.g. hepatic DNA adducts) are currently the most valuable fish biomarkers for ERA. The use of biomonitoring methods in the control strategies for chemical pollution has several advantages over chemical monitoring. Many of the biological measurements form the only way of integrating effects on a large number of individual and interactive processes in aquatic organisms. Moreover, biological and biochemical effects may link the bioavailability of the compounds of interest with their concentration at target organs and intrinsic toxicity. The limitations of biomonitoring, such as confounding factors that are not related to pollution, should be carefully considered when interpreting biomarker data. Based upon this overview there is little doubt that measurements of bioaccumulation and biomarker responses in fish from contaminated sites offer great promises for providing information that can contribute to environmental monitoring programs designed for various aspects of ERA.

Skin ulcers in fish: Pfiesteria and other etiologies

Skin ulcers on fish are one of the most well-recognized indicators of polluted or otherwise stressed aquatic environments. In recent years, skin ulcer epidemics have been either experimentally or epidemiologically linked to exposure to a number of xenobiotic chemicals as well as to biotoxins. Some of these agents, such as toxins produced by the dinoflagellate alga Pfiesteria, have led to serious concerns about the health of aquatic ecosystems, such as estuaries along the east coast of the United States. However, a number of other risk factors besides Pfiesteria have been shown to damage epithelium and may also play important roles in skin ulcer pathogenesis. In addition, increasing evidence indicates that not only may skin damage occur via direct contact with toxins, but it may also be induced indirectly from physiological changes that result from exposure not only to toxins but also to other environmental stressors, such as pH and temperature extremes. The multifactorial pathways that operate at both the ecological and the organismal levels as well as the nonspecific response of the skin to insults make it very challenging to link epidemic skin ulcers to any single cause in natural aquatic populations. Consequently, using pathology to unequivocally identify the specific cause of a lesion (eg. Pfiesteria exposure) is not a valid approach. Only with an increased understanding of the basic mechanisms leading to skin damage (including development of specific biomarkers for specific toxins), along with a better understanding of ecological processes operating in these environments, will we be able to discern the relative importance of various risk factors in skin ulcer development.

Development of newly formed nephrons in the goldfish kidney following hexachlorobutadiene-induced nephrotoxicity

New nephrons developed in goldfish, Carassius auratus, several weeks following hexachlorobutadiene-induced (HCBD) nephrotoxicity. Basophilic clusters of presumptive nephrogenic cells incorporated 5-bromo, 2'deoxyuridine (BrdU) one week after HCBD injection, indicating initiation of DNA synthesis. These clusters, like renal vesicles in the developing kidney, elongated, fused with collecting ducts and developed into immature nephrons during the next 2 weeks. Stereologic quantification showed the volume percent of the kidney occupied by the developing nephrons was greater in HCBD-treated fish 2, 3, 4, and 10 weeks after injection than in the control fish. The presence of large numbers of developing nephrons may provide a marker for renal injury in fish from contaminated waterways.

Oncozoons and the search for carcinogen-indicator fishes

This essay attempts to bring into perspective the importance of hereditary as well as environmental factors as potential causes of neoplasms in feral fishes. Concepts delineated by Knudson regarding hereditary cancers in man and experimental animals will probably be found operative in certain demographic units (oncozoons) among feral fishes bearing neoplasms. Hereditary factors include: antioncogenes (regulatory genes), which act as suppressors of neoplastic expression in homozygous, heterozygous, or hemizygous states, as well as constitutional (structural) genes that influence carcinogen activation or deactivation through enzyme gene products, genes that influence immunologic responses, and gene abnormalities that favor spontaneous or induced mutations. The two major classes of genes (oncogenes and antioncogenes) that influence the manifestation of cancers appear to operate through different mechanisms, but conceivable interactions have not been widely investigated, especially in tumor enzootics among feral fishes. Some explorations have been undertaken in the laboratory by Anders and collaborators in studies of suppressor genes (antioncogenes) and the cellular sarc gene (an oncogene) in melanophoromas in platyfish-swordtail hybrids and backcrosses. Some feral fish oncozoons that exhibit features of hereditary oncodemes as seen in man have been tentatively identified here as candidate systems to be studied more intensively in laboratories, particularly using cytogenetic analysis and breeding methods. In the search for carcinogen-indicator fish species in feral habitats, the traditional approach has been to survey fish populations with the aim of first finding enzootics of fish neoplasia.(ABSTRACT TRUNCATED AT 250 WORDS)