EXECUTIVE SUMMARY
This paper provides a technical evaluation of histopathology as a monitoring tool for the mining industry in Canada, and addresses its role in the determination and monitoring of fish health impacted by those activities. Initially, the paper gives the reader some background concerning diagnostic methodology, the importance of judgment in the process of making a diagnosis, and the effects of temporality on interpretation. Pathology is described in general terms, and the differences between diagnostic or forensic, predictive, experimental, and toxicologic pathology are outlined. Next, the literature review of histopathologic changes in relation to metals and fish organs addresses pathological changes that may be observed using either a light microscope (i.e., a dissecting or normal light microscope), a scanning microscope or an electron microscope.
The methodology for fish histopathology is outlined, including sampling, preservation, submission of specimens and preparation of the sample for shipping, for field and laboratory studies. Histopathology is used in the field in an attempt to define the cause of death in fish die-offs and to define the specific nature of disease patterns so that temporal-spatial comparisons can be made. The process entails evaluation of samples, processing of samples, and reading the slides. The training of the pathologist takes many years and is important in the evaluation process. Comments are made concerning the necessary training for general pathologists and research morphologists, and how the correct training can prevent erroneous results. The importance of training for pathologists and morphologists is emphasized with respect to interpretation and standardization of diagnoses.
Quality assurance in histopathological studies occurs at two levels: Slide preparation and pathological interpretation. Dose-response relationships are necessary to predict a priori the likely outcome of exposure to a specific contaminant. The predictive value of histopathologyvaries from good to excellent in determining the health outcome; however, nothing is more predictive than pathognomonic lesions.
Data gaps encountered in experimental and field studies should be addressed. It is recommended that the determination of organ effects due to metals should encompass as many species as possible and exposure to a wide range of metals at different concentrations. Fish histopathology has a bias toward the effects of metals on gills compared to effects on other organs.
Histopathology, as a tool, has several limitations. Pathology is examined at only one point in time and therefore the changes described are limited to the tissue supplied. Morphological changes can be seen only when the adaptive resources of the fish are exceeded. The relationships of structure and function, adaptation and disease, altered morphology and cause(s), influence(s) of concurrent disease(s), and other confounding variables are given to set the stage for what can be learned using proper collection and preservation techniques.
The report concludes with the recommendation that histopathology be considered in the following circumstances:
- to be used as routine diagnostic assessment technique in the case of fish die-off;
- to help define the background (or baseline) health status of the population;
- to be used in defining the No Adverse Effect Level in laboratory studies on effluent and leachates;
- to be used in operational and post-closure studies only in situations where there are histopathological data present; and,
- not to be used alone.
In conclusion, histopathology is a tool that has not been evaluated fully in monitoring the effects of the mining industry on the health or disease status of fish populations.
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