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Pesticide Residues in Food and Drinking Water: Human Exposure and Risks / Edition 1

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Overview

This book explores human exposure and consumer risk assessment in response to issues surrounding pesticide residues in food and drinking water.

All the three main areas of consumer risk assessment including human toxicology, pesticide residue chemistry and dietary consumption are brought together and discussed.

  • Includes the broader picture - the environmental fate of pesticides
  • Takes an international approach with contributors from the European Union, USA and Australia
  • Highlights the increasing concerns over food safety and the risks to humans

 

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Editorial Reviews

From the Publisher
"...as someone working in the field, I will value this book as an excellent source of fundamental information..." (Chemistry & Industry, 15 Mar 2004)

"...very well-documented..." (International Journal of Environmental Analytical Chemistry, Vol.84, No.14 - 15, 10 - 20 December 2004)

"...a concise and well-organised work..." (Applied Organometallic Chemistry, Vol 19 (9), September 2005)

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Product Details

Table of Contents

Contributors.

Series Preface.

Preface.

1. Introduction (Denis Hamilton and Stephen Crossley).

2. Environmental Fate of Pesticides and the Consequences for Residues in Food and Drinking Water (Jack Holland and Phil Sinclair).

3. Pesticide Metabolism in Crops and Livestock (Michael W. Skidmore and ´ Arpàd Ambrus).

4. Effects of Food Preparation and Processing on Pesticide Residues in Commodities of Plant Origin (Gabriele Timme and Birgitt Walz-Tylla).

5. Toxicological Assessment of Agricultural Pesticides (Mike Watson).

6. Diets and Dietary Modelling for Dietary Exposure Assessment (J. Robert Tomerlin and Barbara J. Petersen).

7. Chronic Intake (Les Davies, Michael O’Connor and Sheila Logan).

8. Acute Intake (Kim Z. Travis Denis Hamilton, Les Davies, Matthew O’Mullane and Utz Mueller).

9. Natural Toxicants as Pesticides (John A. Edgar).

10. International Standards: The International Harmonization of Pesticide Residue Standards for Food and Drinking Water (Wim H. Van Eck).

11. Explaining the Risks (Sir Colin Berry).

Index.

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First Chapter

Pesticides Residues in Food and Drinking Water

Human Exposure and Risks

John Wiley & Sons

Copyright © 2004 John Wiley & Sons, Ltd
All right reserved.

ISBN: 0-471-48991-3

INTRODUCTORY REMARKS

As consumers, we do not want pesticide residues in our food because they have no nutritional value and can potentially pose a risk to health. However, we need pesticides to ensure that a consistent supply of economical and high quality food is available and sometimes residues will remain in the food supply. As a compromise, we require that the amounts of these residues in our food and drinking water will not be harmful to our health and should be no more than absolutely necessary. Risk assessment, which uses scientific processes to meet these requirements, has progressed considerably in recent years.

This book aims to describe the issues surrounding pesticide residues in food and drinking water and, in particular, the issues associated with human exposure and consumer risk assessment. In broad terms, consumer risk assessment encompasses three areas of scientific disciplines - human toxicology, pesticide residue chemistry and dietary consumption - which are explored in further detail within this book.

This chapter will briefly introduce the contents of the book and will discuss some of the commonly asked questions associated with pesticide residues.

WHAT ARE PESTICIDES?

The term 'pesticide' covers a wide range ofsubstances, including insecticides, acaricides, fungicides, molluscicides, nematocides, rodenticides, and herbicides. Pesticides are not necessarily single chemicals of natural or synthetic origin but may be micro-organisms (e.g. fungi or bacteria) or components thereof (e.g. endotoxins from Bacillus thuringiensis), or even so-called 'macro-organisms', e.g. predatory wasps such as Trichogramma evanescens, specifically bred in large numbers to control caterpillars, aphids and other sucking insects. Pesticides are used widely in agriculture since significant economic damage can occur when insects, nematodes, fungi and other micro- and macro-organisms affect food and commodity crops. The quantity and types of pesticides required to ensure high crop yield and unblemished produce acceptable to the consumer vary, depending on climatic conditions, pest species and pest burdens.

Many pesticides of natural origin have been used throughout the history of agriculture. The pesticidal or repellent action of some plants forms the basis of an age-old practice of companion planting, where the proximity of one plant is used to increase the yield of another plant which may be subject to attack by pests. Alternatively, pesticidal extracts from a particular plant type can be applied on or around another to control pests; examples include pyrethrum extracts (from a variety of daisies) or extracts from neem trees (Azadirachta indica). Other naturally occurring inorganic (e.g. arsenic or sulfur) or organic compounds (e.g. nicotine or strychnine) have been used for their pesticidal actions; many of these are extremely hazardous (i.e. poisonous) and pose a significant risk to users and to consumers of the produce, as well as a risk of accidental poisoning.

HISTORY OF PESTICIDE USE AND REGULATION

Large-scale use of pesticides began after World War II with the widespread use of organochlorine and organophosphorus compounds. Other chemical groups were subsequently developed and are used in agriculture today (e.g. triazine herbicides, carbamate insecticides and synthetic pyrethroids). However, pesticides are not a new development and have been used for centuries. For example, sulfur was used in classical Roman times for pest control in agriculture (Smith and Secoy, 1976). In the 19th century, highly toxic, mainly inorganic, compounds of copper, arsenic, lead and sulfur were used for the control of fungal diseases and insects.

HAZARD AND RISK

The World Health Organization (WHO) in 1995 provided specialist definitions for hazard and risk and associated terms such as risk assessment (WHO, 1995). These specialist meanings are used in assessing and explaining the risks of biological and chemical contaminants of food, including pesticide residues. They should not be confused with the normal dictionary meanings of risk and hazard, where the words 'risk' and 'hazard' are often synonymous.

Under the WHO definitions, risk assessment can be split into four different parts. First, in hazard identification, the possible adverse health effects of the chemical are identified from toxicological studies. Secondly, in hazard assessment, the toxic effects and characterization of the biological response in terms of the dose, i.e. the dose-response relationship, are considered and acceptable levels of dietary intake are derived. Thirdly, in exposure assessment, referred to as the 'dietary intake estimate' in this book, the dietary exposure of residues resulting from the consumption of food and drinking water containing residues is estimated. Finally, in risk characterization, the estimated dietary intake is compared with the acceptable levels of dietary intake or dose that were derived as part of the hazard assessment. In simple terms, if the dietary intake is less than this dose, then the risk is acceptable.

SCOPE OF THE BOOK

This section gives an overview and briefly introduces each chapter in the book: environmental fate, metabolism, food processing, toxicology, dietary consumption, chronic and acute dietary intakes, natural compounds, international standards and explaining the risks.

OVERVIEW

Studies of the environmental fate, metabolism and food processing provide basic information for studying residue levels in food. Whereas toxicology describes the hazard, the dietary consumption, in combination with residue levels, provides the dietary intake. Chronic and acute consumer intake estimates compare dietary exposure with acceptable intakes derived from the toxicology. Natural compounds, for proprietary reasons, have not usually been studied as thoroughly as synthetic compounds and therefore the safety of these compounds is frequently less well known. The risk assessment of residues in food must be acceptable at the international level to protect the consumer and to prevent disruption of the international trade in food. The final chapter deals with the very important topic of risk communication.

Most pesticide residues occur in food as a result of the direct application of a pesticide to a crop or farm animal or the post-harvest treatments of food commodities such as grains to prevent pest attack. Residues also occur in meat, milk and eggs from the consumption by farm animals of feed from treated crops. However, residues can also occur in foods from environmental contamination and spray drift. In addition, transport of residues and sediment, e.g. in storm water run-off or leaching through the soil to ground water, may also contaminate drinking water sources.

Since the publication of Rachel Carson's book Silent Spring in the 1960s (Carson, 1965), there has been increased public concern about the impact of pesticides on the environment. Much of this concern was associated with the organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT) and dieldrin. These compounds have both high environmental persistence and high fat solubility which commonly lead to residues occurring in meat, milk and eggs. Most countries have now withdrawn the registration of these persistent organochlorine pesticides. However, residues are occasionally detected in food because of the environmental contamination that remains from historical usage of the chemical. For example, animals grazing on contaminated land readily consume residues, which can be detected in the fat. Grazing cattle may consume 1 kg of soil per head per day and so will ingest the residue directly from the soil as well as residue in the pasture or forage itself. Of the crops grown in soil contaminated with organochlorines, root crops are the most likely to take up residues.

It is possible to estimate dietary intake from the environmental fate, metabolism and food processing experimental data that are commonly submitted by the agrochemical companies. However, these estimates are usually large overestimates of dietary intake as a result of the 'worst-case' assumptions that are included. The most realistic estimate of dietary intake can be obtained by conducting a Total Diet Study. These studies are conducted by a number of countries (WHO, 1999) and many still look at the levels of organochlorine residues in our overall diets. In general, some organochlorine pesticides are no longer detected and the dietary intake of others is slowly declining.

Another potential route by which residues can result in food is through spray drift at the time of pesticide application. Spray drift results in very little residue in our diet since the rate of application is usually far lower than on the directly treated crop. Nevertheless, the contamination can be devastating for an individual farmer whose crops become unsaleable as a result.

Environmental Fate

Studies of environmental fate aim to determine what happens to the pesticide once it has been applied by investigating the behaviour of the compound in soil and water systems. Of particular importance to the overall dietary intake is the potential for the compound to leave residues in water. The environmental properties of pesticides likely to result in contamination of surface water and ground water are persistence, mobility and water solubility. A widely used herbicide such as atrazine has these properties and is frequently detected in surface and ground waters. In contrast to food where most residues result from direct treatment, residues in drinking water usually result from this indirect environmental contamination. Dejonckheere et al. (1996) showed that, even though atrazine was often detected in drinking water in Belgium, its estimated dietary intake constituted only 0.3% of the acceptable level, known as the Acceptable Daily Intake (ADI).

Pesticides are transformed in soil, water and air into metabolites and other degradation products. The transformations may be microbiological (metabolism), hydrolysis (reaction with water) or photolysis (broken down by sunlight). Transformation usually proceeds through small changes to the parent pesticide molecule through to complete mineralization to carbon dioxide, water, chloride, phosphate and so on. For some pesticides, the initial transformation products may also be residues of concern in food or drinking water and should be included in the risk assessment process. Some transformation products are more persistent than the parent pesticide, e.g. dichlorodipenylethylene (DDE) is more persistent than DDT.

Pesticide Metabolism

The metabolism of a pesticide compound is studied by administering a radio-labelled compound to the test animal or the test crop and then, after a suitable interval, examining the distribution of the radio-label. Tissues, milk and eggs are examined in farm animal studies, whereas in plants, the plant foliage, fruit, seeds or roots are examined. The next stage is to investigate the nature of the residue - how much is still unchanged parent pesticide and what are the identities and amounts of metabolites and transformation products. Toxicological decisions are required on which metabolites need to be included with the parent pesticide in the risk assessment and which metabolites can be ignored because their amounts and toxicity are insignificant.

Plant and animal metabolic systems may conjugate the pesticide or a transformation product, i.e. chemically bond it to a natural compound such as a sugar. The conjugate will have different physical properties, e.g. a sugar conjugate is likely to be more water soluble, thus facilitating its elimination by an animal in the urine.

The results of metabolism studies are absolutely crucial before residue and food processing trials can begin. The metabolism studies tell us which compounds must be included in the residue tests of the processed samples. In some cases, the metabolite of one pesticide is another pesticide in its own right, hence suggesting that the risk assessment of the two should be combined.

Food Processing

The level and nature of residues in food can also be affected by commercial or domestic processing and preparation of the food. For example, food preparation will remove surface residues from some foods, e.g. mangoes or citrus, where surface residues are discarded with the peel. Specific studies are commonly conducted to investigate if the nature of the residue changes during processing and how much of the residue remains in the processed products. These food processing studies are a very important aspect of dietary intake estimates, particularly for those commodities that are consumed only after processing, e.g. cereal grains, or substantially after processing, e.g. grapes consumed as wine.

Changes to the nature of the residue during processing and the identification of transformation products, are commonly determined by studying the hydrolysis of the pesticide (reaction with water) at typical cooking temperatures. Hydrolysis experiments tell us which compounds must be included in the residue tests of the food processing studies.

Continues...


Excerpted from Pesticides Residues in Food and Drinking Water Copyright © 2004 by John Wiley & Sons, Ltd . Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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