Title: Food Plants and Chemical Risk
Key words: chemical hazard, toxicity, animal testing, pesticides, organo-phosphates, chronic fatigue syndrome
Date: July 2000
Category: 5. Nutrition and the Environment
Author: Dr M Draper
There are various sources of chemical risk associated with plant foods. This overview of the topic will highlight areas of scientific and popular interest. There has been a great increase in the synthesis and production of chemicals in this century, especially in the past 50 years. Sixty to seventy thousand chemicals are now in regular use and production in the USA increased from 8 million tons a year in 1945 to 107 million in 1985 an increase of 1200% (1).
Chemical Hazard is defined as 'a set of inherent properties of a chemical substance that makes it capable of causing adverse effects when a particular degree of exposure occurs'. There are traditional methods (see Table 1) to test for toxicity that start with animal testing. However, if toxicity and dose-response effects in human-beings are known, such data should take precedence over extrapolation from animal studies. It should also be obvious that whereas laboratory testing usually involves a single chemical, our actual exposure is to the number of chemicals being used in the food chain.
What are the sources of chemical risk in plant foods?
Chemical risk can be defined as ' the probability that a particular adverse effect will occur under specified conditions of chemical exposure'. There are various important factors to consider, such as:
The presence of nutritional deficiencies may compound the risks.The chemical toxicants (see Table 2) can be broken down into four categories
(A) Naturally occurring chemicals present in the plant (phytochemicals) which are intrinsic to the plant or maybe exogenous (e.g. mycotoxins) (see Table 3).
(B) Chemicals added intentionally and purposefully i.e. food additives, nutritional supplements and post harvest treatments. These are easier to define and test for than groups A & D.
(C) Chemicals present purposely but not intentionally e.g. pesticide residues and veterinary drug residues such as hormones and antibiotics.
(D) Chemicals present without purpose and unintentionally such as environmental contaminants in the food chain (both anthropogenic and natural or geological). This category is difficult to quantify or to qualify and the analytical methodology and random testing required to identify chemical substances would be costly and difficult.
Increasing human data about risk to health from pesticides.
Several environmental organisations such as the Environmental Working Group in USA are expressing concern about the exposure of children to organophosphates (2). There is accumulating evidence linking either pesticides or their oestrogen-like breakdown products to the feminisation of animals, for example, or the increase incidence of hormone-related cancers in humans (especially breast cancer in women and prostate cancer in men).
The food pesticide residue may contribute to exposure from other sources, such as in water consumption especially with recycling of river water, which may contain agricultural or industrial contamination. The acute poisoning and chronic fatigue syndromes amongst farmers from known or suspected single or multiple organophosphate exposure is well documented. The obvious question must be whether this form of chemical toxicity plays a part in the growing number of chronic fatigue syndromes we now see in the U.K. Research from Dunstan (3) in Australia presented at the BSNAEM Oxford conference in September 1998 would suggest this is an overlooked area for research into the safety or health risks of widely used chemicals. Low levels of selenium and zinc, for instance, may make the population more susceptible to viruses and the toxic effect of these chemicals.