Michael C. Mix

Cancerous diseases in aquatic animals and their association with environmental pollutants: A critical literature review

This review of the literature on neoplastic or cancer-like disorders in fish and shellfish sets out to (1) summarize what is known of the occurrence of neoplastic diseases in indigenous populations of aquatic animals found in different geographic areas of the world; (2) critically evaluate existing reports so as to determine whether or not environmental pollutants are implicated as causal agents of the cellular disorders and (3) describe the current state of knowledge in the general areas of fish and shellfish metabolism and the use of aquatic animal models in studies of chemical carcinogenesis. Tumors and neoplasms have been described in fish and shellfish populations from many areas throughout the world. Although environmental pollutants have been suggested as the cause of neoplasms in at least some cases, the existing evidence does not permit a firm conclusion. For fish, the quality of the reports and data reviewed varied considerably. There are rather good experimental data to suggest that cancer-like conditions in fish from certain areas of Puget Sound (Washington), the Fox River (Illinois) and Japan are associated with chemical contaminants in the environment. The data purported to support a chemical etiology for highly publicized tumors in fish from the Buffalo River, Torch Lake and Black River are not of a high quality. Most of the studies from those areas are compromised by inadequate experimental designs, and further research will be necessary to achieve a more complete in relation to the existence of tumors in fish from those areas. There are also reports providing impressive evidence that chemical pollutants are not associated with neoplasms in fish, even in those inhibiting environments known to contain mutagenic substances. Large surveys conducted from highly polluted aquatic systems in Yugoslavia (Sava River), Germany (Rhine and Elbe Rivers) and Australia (Port Phillip Bay) all reported negative results. Many other studies and surveys have produced data that neither supported nor refuted a pollution-neoplasm association. In contrast to fish, there is little evidence that neoplasms of clams, oysters and mussels are associated in any significant way with environmental pollution. The most obvious conclusion, from reviewing the existing literature, is that much additional research is required before the relationship(s) between environmental pollution and neoplasms in indigenous aquatic species can be understood. There are severe constraints associated with conducting credible field studies in this area, given the incalculable number of variables in natural environments. In the future, it may be advisable to place more emphasis on laboratory studies employing state-of-the-art methods to provide fundamental information that can be used to understand the nature and causes of neoplasms in aquatic species.

The effects of depuration, size and sex on trace metal levels in bay mussels

Abstract The effects of depuration, size and sex on the concentrations of Mn, Ni, Cu, Zn and Cd were determined for gonadal and somatic tissues of Mytilus edulis from Yaquina Bay, Oregon. After depuration, Mn levels decreased significantly in both tissues while Cu and Ni concentrations increased in somatic tissues. The latter finding may have been associated with a stress response manifested by the appearance of new byssal threads and attachment to the vessel. Larger, and presumably older, mussels contained higher concentrations of Ni, Cu and Cd in their somatic tissues while smaller animals had greater somatic levels of Mn. There were no significant differences in gonad concentrations between the two size groups. Manganese and Zn levels were greater in the gonads of female mussels and Cd was more concentrated in the somatic tissues of females.

Concentrations of unsubstituted polynuclear aromatic hydrocarbons in bay mussels (Mytilus edulis) from Oregon, USA

Abstract Concentrations of fifteen unsubstituted polynuclear aromatic hydrocarbons (PNAH) were measured in Mytilus edulis from two sites in Yaquina Bay, Oregon, USA, during 1979–1980. There were significant differences in PNAH levels between the two populations. The average total concentration in mussels inhabiting the more industrialized bayfront was 986·2 μg/kg compared with 273·9 μg/kg in mussels from a more remote site across the bay. Substantial differences were found in the concentrations of different PNAH in M. edulis examined during this study. The smaller more water soluble, compounds were concentrated to one or two orders of magnitude above the larger, less soluble PNAH.

Uptake and accumulation of naphthalene by the oyster Ostrea edulis, in a flow-through system

A flow-through system was used to follow naphthalene and naphthalene metabolite accumulation in the seawater and in the tissue of the oyster Ostrea edulis. After 72 h, 82.5% of the naphthalene carbon was recovered from the system. Glucose was added to seawater to stimulate the pathways of glucose metabolism in the oysters. Streptomycin (100 ppm) reduced microbial oxidation of naphthalene and glucose, and reduced bacterial growth. However, even in the presence of streptomycin, microbial oxidation of naphthalene was considerable. The main oxidation product recovered from seawater was 14CO2. Radioactivity was also associated with compounds which separated by TLC with 2- and 1- naphthol. The pattern of naphthalene uptake and accumulation in oyster tissues was relatively constant after only a few hours of exposure to naphthalene. The potential of tissues to accumulate naphthalene was shown to be a function of multiple variables such as nutritional state, lipid concentration, length of exposure to naphthalene, and the external naphthalene concentration. Carbon-14-labeled metabolites derived from 14C-naphthalene were consistently recovered from digests of the oyster tissues. Non-CO2 alkaline-soluble substances were the primary metabolites. Hexane-extractable substances, which separated by TLC with known standards of 2- and 1- naphthol, were consistently recovered from seawater and tissue digests. It was not possible to conclude that these metabolites were a result of naphthalene metabolism by oyster enzyme systems.

Shellfish diseases in relation to toxic chemicals

Abstract Diseases of shellfish are often classified as either infectious or noninfectious. While little is known about the influence of toxic chemicals on infectious diseases, some information is available on negative effects of xenobiotics on certain cellular and physiological functions, which may lead to disease. Early studies described gross and histopathological alterations caused by high concentrations of different chemicals. Subsequently, finer biological resolutions, including the effects of toxic substances on different tissues, cells, and physiological and biochemical processes in these animals, were obtained. Nevertheless, there are still only primitive perceptions about the exact relationships between toxic chemicals in the environment and the possible diseases they may cause in shellfish. Consistent with modern concerns about the impact of chemical mutagens and/or carcinogens in the aquatic environment, research has been concentrated on neoplastic diseases in shellfish populations from different geographic areas of the world. A common hypothesis, underlying approaches to this research, has been that cancerous diseases in clams, oysters and mussels may be caused by chemical pollutants present in the environment they inhabit. Results which support this hypothesis do not dominate the literature. Some studies of clams and mussels do not preclude a possible causal role for toxic chemicals. However, different studies have shown that shellfish inhabiting exceedingly polluted environments did not have neoplasms, whilst others revealed that neoplastic diseases were present in mussels from essentially pristine areas. Further research is necessary to achieve a more complete understanding of the association between toxic chemicals in the environment and diseases, including neoplasia, in indigenous shellfish populations.

Observations on the ultrastructure of large cells associated with putative neoplastic disorders of mussels, Mytilus edulis, from Yaquina Bay, Oregon☆☆☆

Abstract Large cells, generally thought to be associated with neoplastic disorders in bivalve mollusks, were studied with the electron microscope. The atypical cells had an average diameter of 15 μm and a nuclear to cytoplasmic ratio of about 1–1.5. Nuclei were extensively pleomorphic and bizarre shapes were common. Nucleoli were prominent and often multiple. In the cytoplasm of the large cells, there was a wide range of variability in anomalous organelles. Two cell types were originally thought to exist; however, it is now thought that the two cell types represent the two extreme morphological expressions of a single cell line. Their varying appearance is correlated with the density of ribosomes and abundance of cellular organelles. The large Mytilus edulis cells possess many ultrastructural properties that are characteristic of certain malignant vertebrate cells. However, alternative explanations for their structure and function are also possible.

Notes. A simple and inexpensive method for measuring integrated light energy.

The ozalid technique is a simple and inexpensive method for measuring integrated sunlight energy in the field for periods up to a maximum of 1 day. This paper describes a modification of the ozalid technique that makes it suitable for long-term light measurements. Data from the modified ozalid meter were calibrated against an Eppley Precision Spectro Pyranometer, yielding a strong positive correlation (R/sup 2/ = 0.97).

Proliferative characteristics of atypical cells in native oysters (Ostrea lurida) from Yaquina bay, Oregon☆

Abnormal, large, possibly neoplastic cells from two Ostrea lurida have been successfully labeled with tritiated thymidine, and thus, for the first time, data are available for analyzing a presumptive invertebrate proliferative disorder. Large numbers of labeled atypical cells (AC) were uniformly distributed throughout the connective tissue (CT) underlying the gills, mantle, stomach, gut, digestive diverticula, kidney, and gonad. Two general types of AC are associated with the proliferative disorder. Both are abnormally large with many features characteristic of undifferentiated cells, and both are probably members of a proliferating compartment. The labeling index (LI) for AC ranged from 1.22% in connective tissue surrounding digestive tubules to 14.17% in CT underlying gill epithelium; the LI for all AC was 4.82%. The data strongly suggest that the AC proliferate at a much greater rate than any other oyster cells subjected to similar treatment.

Benzo(a)pyrene concentrations in somatic and gonad tissues of bay mussels, Mytilus edulis.

Concentrations of Benzo(a)pyrene(PAP) were measured in somatic and gonadal tissues of M. edulis in Yaquina Bay, Oregon over several months to determine whether or not changes in levels in these tissues could account for winter-spring fluctuations in BAP concentrations. The period of high January-February concentrations was of special interest.

Neoplastic disease in bivalve mollusks from Oregon estuaries with emphasis on research on proliferative disorders in Yaquina Bay oysters.

Studies were conducted on oysters (Ostrea lurida) in Yaquina Bay, Oregon, to determine seasonal effects on proliferative disorders, correlation between onset of the condition and age of oysters, and the exact nature of the proliferative disorders. Imported oysters were planted at various locations; the mortality was monitored and monthly histological examinations were made. Results indicated that the disorders did not occur in significant numbers of oysters. There were occasional, small, late-summer oyster mortalities associated with increased water temperature and blooms of Vibrio bacteria. There was no definitive evidence to indicate whether the proliferative disorder caused mortality of the affected oysters. (HLW)