Coastal and Estuarine Risk Assessment - Chapter 9 pdf

©2002 CRC Press LLC

The Use of Toxicity

Reference Values (TRVs)

to Assess the Risks That

Persistent Organochlorines

Pose to Marine Mammals

Paul D. Jones, Kurunthachalam Kannan,

Alan L. Blankenship, and John P. Giesy

CONTENTS

9.1 Overview

9.2 Introduction

9.3 Problem Formulation

9.4 Exposure Assessment

9.4.1 Exposure Assessment Methods

9.4.2 Estimating Exposure through Modeling

9.4.3 Measuring Internal Dose Using Tissue Residues

9.5 Effects Assessment

9.5.1 Adverse Effects in Marine Mammals

9.5.2 Immunotoxicological Studies in the Harbor Seal

9.5.3 Toxicological Studies in Cetaceans

9.5.4 Exposure Studies in Mustelids

9.5.5 Toxicity Reference Values

9.5.6 Toxicity Threshold Evaluation

9.5.7 Uncertainties in TRV Determination

9.6 Risk Characterization

9.6.1 Risk Assessment Based on New Zealand Data

9.7 Conclusions

Acknowledgments

References

9

©2002 CRC Press LLC

9.1 OVERVIEW

Marine mammals are known to accumulate relatively high concentrations of persistent

organochlorine contaminants (POCs). These stores of contaminants have the potential

to act as a continuing source of elevated exposure to these organisms. Although a

considerable amount is known about the concentrations of POCs in marine mammals

and about the processes that lead to their accumulation, little is known about the

potential these contaminants have to cause adverse effects in exposed animals.

Although several anecdotal studies have measured relatively high POC concentrations

in marine mammals associated with mass mortality events, in all cases, it has been

difficult to demonstrate a cause–effect relationship.1,2 Similarly, several semifield

studies have been conducted by feeding naturally contaminated fish to captive animals

and assessing adverse effects.3,4 It is also difficult to attribute effects of organochlo￾rines in these studies due to small sample sizes and the presence of co-contaminants

in the food source used for feeding. To determine possible adverse effect levels in

marine mammals, we previously compiled a number of the most relevant and rigorous

studies to derive toxicity reference values (TRVs) for marine mammals.5 In this

chapter, we use these TRVs to evaluate the possibility of adverse effects in marine

mammals at current levels of exposure. The data chosen for the assessment were

collected in New Zealand. These data were chosen because they provide detailed

information on a wide range of dioxin-like contaminants for a variety of species and

are coupled with equivalent information for a variety of other environmental matrices.

The New Zealand data represent one of the lower levels of exposure known to occur

for marine mammals, providing a conservative estimate of possible risks to other

marine mammal populations. Risks seem to be greatest for marine mammals feeding

in inshore habitats presumably due to the higher concentrations of anthropogenic

pollutants in these locations. Since there are identifiable levels of risk to marine

mammals in the relatively pristine southern oceans, there appears to be little global

capacity for the dissipation of additional POCs.

9.2 INTRODUCTION

The U.S. EPA has developed a framework for ecological risk assessment (ERA) that

consists of four phases: (1) problem formulation, (2) exposure assessment, (3) effects

assessment, and (4) risk characterization.6 The problem formulation step is a formal

process to develop and evaluate a preliminary hypothesis concerning the likelihood

and causes of ecological effects that may have occurred, or may occur.

6 A key step

in the problem formulation phase is the development of a conceptual model detailing

exposure pathways and key receptor organisms. In the exposure assessment phase,

the potential for adverse effects to ecological receptors due to chemical stressor

exposure is assessed by evaluating the probability of co-occurrence of the stressors

and the ecological receptors considered.6 The effects assessment evaluates effects

data to assess (1) the link between elicited effects and stressor concentrations, (2) the

relationship between the elicited effects and the associated assessment end point,

and (3) the validity of the exposure model (i.e., are conditions under which the

effects occur consistent with the conceptual model?6). In the risk characterization