Food Chemical Safety

Volume 1: Contaminants

David Watson

• Publisher: Woodhead Publishing
• Year: 2001
• Print ISBN:
  9781855734623
• eBook ISBN:
  9781855736320
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Chemical contaminants in food, from pesticides and veterinary drug residues to contamination from food packaging, are a major concern for the food industry. Written by a distinguished international team of contributors, this authoritative collection describes the main chemical contaminants, their health implications, how they contaminate food products, methods of detection and how such contaminants can be controlled. - Describes the main chemical contaminants of food, their health implications, how they contaminate food products, methods of detection and how such contaminants can be controlled

1

Introduction

D. Watson Food Standards Agency, London

1.1 Background

Scientific knowledge about chemical contamination of food has grown considerably in recent years. Only a few years ago I wrote that ‘the study of chemical contaminants in food is still a relatively young science’ (Watson, 1993). Since then this area of science has continued to develop, in particular becoming an established part of regulatory reviews of food safety across the world. Chapters 12 to 14 of this book describe this major new development. Chapters 2 to 5 detail growing development of practical methods of detecting, monitoring and managing chemical contamination of food. Practical methods of working on these substances have developed steadily. The middle chapters (6 to 11) summarise and review information about the different types of chemical contaminants.

The main groups of chemical contaminants that can be found in food share the following characteristics:

• They are not intentionally added to food.

• Contamination can happen at one or more stages in food production.

• Illness is likely to result if consumers ingest enough of them.

The first of these points distinguishes chemical contaminants from other chemicals in food, e.g. vitamins and additives. The wide range of possible sources of chemical contamination has major resource implications, particularly in controlling chemicals that find a wide range of uses, for example pesticides as opposed to veterinary drugs. In order to ensure consumer and worker protection very careful attention must be given at all stages in food production, unless it is known that contamination with a particular chemical cannot occur at some stages.

We know most about residues in food of chemicals such as pesticides and veterinary drugs that are used in food production. Companies that produce these chemicals are generally required to convince the licensing authorities that there will not be unsafe levels of residues in food, if the products containing the chemicals are used as instructed. This requirement has generated a huge amount of information, some of it now in the public domain. Less is known about toxins that occur naturally in food, although there has been much chemical research on toxins produced by fungi (mycotoxins).

1.2 Pesticides

Many pesticides have been tested for in food. Organochlorine chemicals, such as DDT, have been included in surveys for residues of pesticides in food for many years. The detection of DDT and related compounds in the environment in the 1960s led to concern that their environmental persistence might cause widespread and lasting damage to ecosystems. Indeed their presence in the environment was linked with reduction in eggshell thickness and hence reduced breeding success of birds of prey. Such concerns led to surveillance for residues of persistent organochlorine pesticides in environmental and food samples. Group detection of these compounds by a common method of analysis aided this surveillance. It also generated data on chemically related compounds that are not pesticides, notably polychlorinated biphenyls (PCBs; see section 1.4), and demonstrated environmental contamination by phthalate esters (section 1.6). The latter esters probably contaminated food samples in the laboratory. PCBs proved to be very persistent contaminants in the environment.

Environmentally persistent organochlorine pesticides such as DDT have largely been replaced as insecticides by organophosphorus compounds. This change has brought its own problems. Concerns about possible effects of organophosphorus pesticides on users is leading to their replacement by yet other pesticides such as pyrethroids that are thought to be less hazardous to man and the environment. In the case of pyrethroids their ‘green’ image derives from their origins in ancient usage of chrysanthemum (pyrethrum) products for a variety of purposes. Natural origin of chemicals in food does not mean that the chemicals are safer than residues of man-made ones in what we eat.

The control of pesticide residues in food is done via the law in many countries. There is little variation between national laws in this area, but the way the law is applied differs between countries. As for pesticide residues, so also for other aspects of the chemical safety of food, global harmonisation of food law is a distant prospect. This is despite considerable effort in some groups of countries to achieve consistency, for example in the European Union, the MERCOSUR group (Argentina, Brazil, Paraguay and Uruguay) and the Australia New Zealand Food Authority. The FAO/WHO Codex Committee on Pesticide Residues (CCPR) and the Joint Meeting on Pesticide Residues (JMPR) have worked for many years towards globally accepted standards for pesticide residues in food, but only recently have these started to be adopted in countries. For all pesticides in food it is essential to check that any residues in food are within maximum residue limits or other standards provided these are based on extensive toxicological testing of the chemicals involved. Maximum residue limits for pesticide residues in food are set by many internationally recognised authorities, notably the European Union, the US Food and Drugs Agency, and the world bodies CCPR and JMPR.

A wide range of practical steps can be taken to control pesticide residues in food, including the following:

• Make information available to consumers so that they can make an informed choice. It is essential that consumers are properly informed about the food that they purchase. Apart from the fact that this is one of their basic rights, communication on food safety that is poor or absent can lead to ‘scare stories’ in the media with consequential concern for consumers and money lost by food suppliers.

• Control the availability and usage of pesticides. A particularly effective method in theory, since it applies at source. This is not necessarily true in practice. If there is an urgent need to control a pest or even where the need is not pressing but the user is several stages divorced from the consumer, there is always the potential for more pesticide to be used than is actually needed, or for the pesticide to be misused (e.g. applied too close to harvest or slaughter).

• Limit food contamination by pesticides present in the environment. It is important to recognise that the use of pesticides near to crops and farm animals, and in factories concerned with food production, can lead to residues in food. Obviously this can be particularly difficult to detect if surveillance for residues looks mainly for those pesticides used directly on crops or farm animals. The remedy is to extend surveillance and to remind users to be very careful to avoid adventitious contamination of food at all stages of production right through to marketing.

• Police limits for pesticides in food. Global standard setting may be advancing but it is essential that there is effective surveillance. This must include action as well as monitoring.

• Advice of the type noted above on avoiding adventitious contamination of food needs to be made both nationally and by management in companies involved with food. The control of pesticide residues in food could include HACCP (Chapter 11) to provide an important element of prevention. Other preventative methods include testing of incoming supplies of raw and other materials, and direction by retailers to suppliers that they must use only a defined list of pesticides in specified ways.

• Halt the supply of contaminated food. This rather draconian measure can and has been used in extreme cases. In the UK there are measures in place to do this in the Food and Environment Protection Act 1985.

• Apply an open and objective system of controlling the use, safety and availability of pesticides.

Only where all of these approaches are used is there likely to be the chance of convincing consumers that they are protected against unsafe levels of pesticides in food. Many consumers have now been influenced by the media to think that all residues of pesticides in food are unsafe. This has contributed to the growth in demand for organic food.

1.3 Veterinary drugs

Like pesticides, veterinary drugs have an important role to play in reducing disease and suffering but their use has been brought into question by concerns about residues of them in food. The fact that their use can lead to residues in the food supply was recognised rather later than for pesticide residues. Nevertheless, methods of analysis and surveillance for veterinary drug residues are now well established in many parts of the world.

The main classes of veterinary drugs used in farm animals are:

• Ectoparasiticides used to control flies, ticks and other skin parasites. These fall under the general heading of pesticides (section 1.2 above).

• Antimicrobial agents which are used to treat and prevent diseases caused by bacteria and fungi.

• Anthelmintic agents used against worms and flukes (hence the name – helminths include liver flukes).

• Anabolic agents to promote growth. This group includes hormones and some antimicrobial substances.

• Tranquillisers and beta-agonists which have been used to reduce the risk of harm to animals being taken to slaughter.

• Coccidiostats to treat and prevent coccidial parasites in the GI tract.

Antimicrobial agents are of two general types – antibiotics and chemotherapeutic agents. The first of these inhibits microbial growth, the second kills the micro-organisms. Residues of antibiotics have been screened by testing of milk, meat or kidney samples to see if they inhibit microbial growth. This simple, direct approach has been used widely. The testers need to take account of possible false positive results if the sample contains a natural inhibitor, and the variable sensitivity of bacteria used in the test to different antibiotics. The use of chemical methods to measure residues of antibiotics has not been as popular, mainly because they are more labour intensive and hence more expensive than microbial inhibition tests. However, some antibiotics, such as sulphonamides, are not readily detected by bacterial tests. Chemical methods are essential for chemotherapeutic antimicrobial agents, such as chloramphenicol, since they are not detected effectively by bacterial inhibition.

Residues of antimicrobial agents tend to be present at their highest levels in the liver and kidney, as well as the site of injection (if that is the route of application). The liver is the main site of biochemical modification of antimicrobial substances, as the body tries to convert them to less toxic compounds. Indeed, the body tries to do this to all substances that are foreign to the body. The kidney, as one of the two main sites of chemical excretion, the other being the GI tract, is therefore a good organ to te...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributors
• 1: Introduction
• Part I: Analytical methods
• Part II: Particular contaminants
• Part III: Regulation
• Index