A Methodology for Inferring the Causes of Observed Impairments in Aquatic Ecosystems

Abstract

Biological surveys have become a common technique for determining whether aquatic communities have been injured. However, their results are not useful for identifying management options until the causes of apparent injuries have been identified. Techniques for determining causation have been largely informal and ad hoc. This paper presents a logical system for causal inference. It begins by analyzing the available information to generate causal evidence; available information may include spatial or temporal associations of potential cause and effect, field or laboratory experimental results, and diagnostic evidence from the affected organisms. It then uses a series of three alternative methods to infer the cause: Elimination of causes, diagnostic protocols, and analysis of the strength of evidence. If the cause cannot be identified with sufficient confidence, the reality of the effects is examined, and if the effects are determined to be real, more information is obtained to reiterate the process.

A method for assessing causation of field exposure–response relationships

“…That process uses qualitative scoring of the characteristics of causal relationships to organize and weigh evidence for and against a general causal hypothesis. Defining the scoring criteria reduces lapses in consistency and provides transparency when weighting evidence for assessment of either general or specific causation [8,18]. The method has been applied to determining whether the water quality benchmark for conductivity is based on a causal relationship [13,20].…”

“…One to three plus or minus symbols are used to indicate the weight of a piece of evidence; (þ þ þ) or (À À À) indicates convincing support or weakening, (þ þ) or (À À) indicates strong support or weakening, (þ) or (À) indicates some support or weakening, and (0) indicates no effect. These qualitative scores were developed for epidemiology [18] and adopted for ecoepidemiology [4,8].…”

“…Ecoepidemiologists tend to be concerned with specific causation (what is the cause of impairment of a particular population or ecosystem?). As a result, ecoepidemiological methods are well developed for specific causation, particularly in the Causal Analysis/ Diagnosis Decision Information System [7,8]. However, in the present study, we present a method for addressing general causation.…”

Linking Regional and Local Risk Assessment

“…The approach suggested here involves the construction of several lines of evidence (comparisons between measured concentrations and toxicity endpoints from toxicity tests, biomarkers, biological surveys, etc.). The different lines of evidence should then be evaluated in a formal and systematic way with a weight-of-evidence approach (Suter and Barnthouse 1993, Menzie et al 1996, Hull and Swanson 2006 that uses a collection of epidemiological criteria to evaluate causality (Hill 1965, Fox 1991, Suter et al 2002.…”

Need for establishing integrated programs to monitor endocrine active compounds

“…In addition, however, a weight-of-evidence approach will have to be used to reduce the level of uncertainty. Several investigators have proposed criteria which can help to make a case for causal inference and to evaluate whether wildlife populations have been affected by EACs [4,12,57,58]. An example of such criteria is provided by the work of Ankley and Giesy [60], who suggested the following criteria for establishing cause-effect relationships: (1) documentation of effects in individuals, (2) documentation of adverse effects in populations, (3) coherence between effects observed in populations vs. those in individuals, (4) identification of a plausible mechanism of action consistent with effects in individuals (possibly through laboratory studies-see above), (5) positive identification of specific contaminants operating through this mode of action (possibly by combined bioanalytics/chemical analytics-see above), (6) reasonableness of dose-response relationships, (7) evidence of the recovery of populations or individuals upon removal of the stressor.…”