Bioaccumulation of Xenobiotic Compounds

Des W. Connell

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315891026
• eBook ISBN: 9781351087025
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Environmental Science

One of the very few - if not only - books written exclusively related to this topic. This book comprehensively outlines the principles governing the accumulation of chemicals from the environment by organisms. Packed with tables and diagrams, this work reviews the experimental data available on both terrestrial and aquatic systems. It describes methods which are used to predict bioaccumulation of chemicals from their physicochemical properties. It also reviews environmental and other factors influencing bioaccumulation. This text also includes previously unpublished theoretical explanations of several bioaccumulation processes, including food chain biomagnification. Information in this exceptional volume is useful to government officials involved with environmental management, chemists, biologists, consultants working with chemical waste control, researchers, and graduate students.

Chapter 1

INTRODUCTION

Des W. Connell

TABLE OF CONTENTS

I. Xenobiotic Chemicals and Bioaccumulation

II. Historical Development of Knowledge on Absorption, Bioaccumulation and Related Effects of Xenobiotic Chemicals

III. Importance of Bioaccumulation in Environmental Management

References

I. Xenobiotic Chemicals and Bioaccumulation

Xenobiotic chemicals are chemicals foreign to life, which are usually derived synthetically or from an abiotic process. The term “xenobiotic” is a combination of the Greek words “xenos”, meaning strange or foreign, and “bios”, meaning life. Thus xenobiotic chemicals are pollutants in the biosphere although not all pollutants are xenobiotic chemicals. The synthetic xenobiotic chemicals are often of enormous value to human society, and are usually the majority of the chemicals in such important groups of substances as pharmaceuticals, petrochemicals, pesticides, and plastics. Schmidt-Bleek and Haberland¹ in 1980 reported that there were 40,000 chemicals commercially available, and 2,000 were placed on the market in addition each year.

Since the very beginning of the chemical industry there has been interest in producing more efficacious products. This has led to continuing research into the prediction of the likely properties of a chemical prior to its use. Concurrently, research has been in progress which will give a better understanding of the mode of action of chemicals. One of the most important properties of a chemical, in situations involving a biological effect or application, is how well it is absorbed or bioaccumulated. Bioaccumulation usually means the accumulation of a chemical in an organism to a higher concentration than is present in an external source.

II. Historical Development of Knowledge on Absorption, Bioaccumulation and Related Effects of Xenobiotic Compounds

The basis of our understanding of bioaccumulation was developed by scientists working in the 1870's who discovered some of the principal phenomena governing the behavior of chemicals in gases, water, and other phases. Some of these principles are now used in contemporary investigations of the behavior of chemicals in the environment and in organisms. For example, Berthelot and Jungfleisch² in 1872, and Nernst³ in 1891, discovered that a constant partition coefficient, or “distribution ratio”, controlled the partitioning of a single pure chemical between two different phases. This knowledge marks an important step forward, since once the partition coefficient is known for a compound, its distribution between the same phases in other situations can then be calculated. The bioaccumulation of a chemical by an organism can be seen, in many situations, as a partition process.

During this early time period, interest was not only developing in aspects of chemical behavior, but also in the behavior of drugs, poisons, and narcotics in organisms. Thus, during this pioneering period, others were building on the basic physicochemical knowledge available, and utilizing this in attempting to elucidate the factors governing the physiological properties of chemical compounds. Probably the earliest among these were Crum-Brown and Fraser,^4,4,3 who in 1868-1869 proposed that the physiological action of a compound was a function of its chemical constitution. Later in 1893, this found practical expression in the work of Richet,⁶ who found that the toxic effects of certain ethers, alcohols, aldehydes, and ketones were inversely related to their solubility in water.

A few years later, interest was first kindled in the partition behavior of nonelectrolyte chemicals in relation to their physiological effects on organisms. The English born and Swiss-trained Charles Ernest Overton commenced his research program into the relationship of physicochemical properties of compounds to their narcotic effect on organisms virtually single-handedly. Also about this time, Hans Meyer and his collaborator Fritz Baum were active in the same field. A series of papers^7,8,9 were published by these gifted researchers culminating in 1901 with the publication of Overton's book, Studien Uber Die Narkose¹⁰ (Studies of Narcosis). This book is a landmark in studies of how physicochemical properties of chemicals influence their physiological effects on organisms. It sets out many of the basic principles which have been continually refined and expanded up to the present day.

One of the major discoveries of these researchers was that the narcotic action of a nonelectrolyte is correlated with the compound's lipoid substance-to-water partition coefficient. Overton's studies were carried out with 130 compounds including alcohols, hydrocarbons, nitriles, nitroparaffins, aldehydes, and ketones, and with a variety of test animals including tadpoles, fish, Crustacea, and Daphnia.

In 1904, Traube¹¹ extended the physicochemical properties of interest from the partition coefficient to surface tension when he established a linear relationship between surface tension and activity for a series of narcotics. Aspects of structural organic chemistry were introduced by Fuhner,^12,13 who noted a possible relationship between narcotic activity and the number of carbon atoms in a compound.

A considerable volume of data was accumulated in the following years, confirming the general accuracy of the previously developed relationships. However, during the 1950s and 1960s further significant refinements and developments occurred. Hansen and Leo,¹⁴ together with a variety of co-workers, suggested the use of the octanol to water partition coefficient (K_ow) as the most suitable partitioning phase pair for studying the relationship between partition coefficient and the biological properties of compounds. They systematized much of the information available into quantitative structure activity relationships (QSAR).

Initially, this group developed the following equation for toxicity:

$\log \left(1/\text{C}\right)={\text{k}}_{\text{1}}\text{π}\text{+}{\text{k}}_2\text{σ}\text{+}{\text{k}}_3$

where C is the molar concentration of a compound producing a standard response in a constant interval; k₁ k₂, and k₃ are empirical constants; ir is log P_x — log P_H, where P_x is the octanol-to-water partition coefficient of a derivative and P_H is that of a parent molecule; and σ is the Hammett constant.

When k₂ is equal to zero, this equation is equivalent to the Meyer-Overton relationship, which predicts a linear relationship between log(l/C) and the octanol to water partition coefficient. When k₂ has an empirical value, the Hammett constant is included in the relationship and provides a much better correlation for many compounds with toxicity than the Meyer-Overton relationship mentioned above. It is noteworthy that the relationship between the Hammett constants alone and toxicity is not particularly strong. Later, this linear relationship was developed by Hansch¹⁵ into a parabolic form expressed by the following equation:

$\log \left(1/\text{C}\right)=-{\text{k}}_{\text{1}}{\left(\log {\text{K}}_{\text{ow}}\right)}^2+{\text{k}}_{\text{2}}\left(\log {\text{K}}_{\text{ow}}\right)+{\text{k}}_{\text{3}}\text{σ}+{\text{k}}_{\text{4}}$

where k_ow is the octanol to water partition coefficient and k₁, k₂, k₃ and k₄ empirically developed constants. This relationship has been extensively and successfully used to explain the toxicity of a variety of compounds.

Up to the period of these developments, studies of the uptake and behavior of xenobiotic chemicals in organisms was principally concerned with relatively short-term effects, such as toxicity and narcosis. The applications were mainly concerned with pharmaceuticals and their effectiveness in relationship to human health. In the 1960s widespread concern developed regarding the use of persistent chemicals in the environment. Much of this related to the chlorinated hydrocarbons, particularly DDT. These substances tend to have little effect in the short term, but trace residues bioaccumulated within organisms over long periods have had adverse effects, in many cases. As a result of this, there was a developing interest in the presence of persistent chemical residues in organisms, and the routes and mechanisms of entry of these substances. Accumulation through steps in the ecological food chain, with progressive increases in concentration, was initially proposed as the mechanism of entry for many organisms. With terrestrial ecosystems the presence of contaminants in food must be the principle source of residues in organisms. However, in aquatic ecosystems water to organism partitioning has been found to be a significant influence on the presence of residues in organisms within the system. In principle, it could be expected that the biological response of bioaccumulation with environmental xenobiotic compounds would be related to the factors generating the biological response observed with pharmaceutical xenobiotic compounds such as drugs, narcotics, and so on. Thus, it could be expected that the bioaccumulation of environmental xenobiotics would be related in some way to the octanol-to-water partition coefficient of the compounds involved.

The general characteristics of the interaction of xenobiotic chemicals with organisms can be seen in simplifie...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Chapter 1 Introduction
• Chapter 2 Evaluation of the Bioconcentration Factor, Biomagnification Factor, and Related Physicochemical Properties of Organic Compounds
• Chapter 3 General Characteristics of Organic Compounds Which Exhibit Bioaccumulation
• Chapter 4 Environmental Routes Leading to the Bioaccumulation of Lipophilic Chemicals
• Chapter 5 The Partition Mechanism
• Chapter 6 Bioconcentration of Lipophilic and Hydrophobic Compounds by Aquatic Organisms
• Chapter 7 Biomagnification of Lipophilic Compounds in Terrestrial and Aquatic Systems
• Chapter 8 Bioaccumulation of Metallic Substances and Organometallic Compounds
• Chapter 9 Achievements and Challenges in Bioaccumulation Research
• Appendix
• Index