With glyphosate being in the non-agricultural media over the past few months it is a good time to look at chemical residues in food and explain how acceptable levels are determined for various food types.
Chemical residues will be found in all foodstuffs. When herbicides, fungicides and insecticides are applied to a crop or pasture, they break down over time into other chemicals. The quantity and nature of these chemicals (residues) will vary between the type of chemical and the environment to which they are exposed.
Setting allowable levels of chemicals in foods
The Australian Pesticides and Veterinary Medicines Authority (APVMA) determine the maximum residue limits (MRL) for agricultural and veterinary chemicals in agricultural produce. Pesticide labels are designed to ensure that the use of those pesticides does not lead to higher than the determined MRLs in foodstuffs.
Not exceeding MRLs is extremely important to protect the environment, human health and trade.
The three main steps in assessing the safety of agricultural and veterinary chemicals in food are:
- Toxicological – scientists review large numbers of animal feeding studies to evaluate short and long-term risk of consuming different chemicals. These studies help determine the No Observable Effect Level (NOEL) which is used to set the acceptable daily intake for a chemical. The NOEL used to set the acceptable daily intake is generally that for the most sensitive animal species in the studies.
The Acceptable Daily Intake (ADI) – is the amount of chemical that can be consumed every day for an entire lifetime without an appreciable increase in risk to health.
The Acute Reference Dose (ARfD) – is an estimate of the maximum amount of a chemical in food or drinking water expressed as milligrams per kilogram of body weight that can be consumed in one meal or one day without an appreciable increase in risk to consumer health.
- Maximum residue limit (MRL) – is the highest concentration of a chemical residue that is legally permitted or accepted in a food or animal feed. Concentration is expressed in milligrams per kilogram (mg/kg) of the commodity. Australian MRL Standard (Schedule 20) can be found at the Federal Register of Legislation website . A list of global MRL databases can also be found at the Department of Agriculture website . The APVMA determines the MRL after a comprehensive analysis and calculates the minimum amount of pesticide required for effective control and that leaves minimal or no residue on the commodity. This data also helps set appropriate harvest and export withholding periods for the pesticide.
- Dietary exposure – the APVMA uses the MRL to conduct a dietary exposure evaluation. Food Safety ANZ (FSANZ) conducts a review and undertakes public consultation before incorporating the MRL into Australian Food Standard Schedule 20.
National and state-based surveys are also carried out to monitor residue levels in food
- National residue survey (NRS) – conducted by the Commonwealth Department of Agriculture and Water Resources to manage the risk of chemical residues and environmental contaminants in Australian animal and plant products. It aims to provide an estimate of residues in products, confirm that residues in products are below set limits and alert responsible government authorities and industry, if limits are exceeded.
- Australian total diet study – Food Standards Australia New Zealand monitor the food supply to ensure that existing food regulatory measures provide protection of consumer health and safety. It is conducted every two years with samples collected by state and territory food regulatory agencies.
- State surveys – State and Territory government agencies conduct surveys when there is a perceived risk. If residues are above the legal limit they are investigated and action taken.
- Industry surveys – industry groups conduct surveys usually as part of a quality assurance program such as Freshcare and Livestock Production Assurance (LPA) . Some retailers such as Coles and Woolworths will also conduct their own testing.
Despite Australia having some of the highest quality food in the world there is still distrust in the general community.
Some of this is pushed by media because a perceived problem gets more clicks than a positive story. Also, some sections of the non-conventional food production system are looking for a marketing edge.
If you read the blog previously about the loss of faith in science there is a reference to the US Environmental Working Group (EWG) who found detectable levels of glyphosate in breakfast cereal. EWG have a very engaging website and uses lots of emotive language. It is interesting to note that their stated allowable daily intake (ADI) of glyphosate is set at 0.01 mg per day. This is 110 times lower than even the Californian Environmental Protection Agency which is renowned for its strict control of chemicals. Table 1 shows the ADI set by different organisations.
Table 1 Allowable daily intake of glyphosate (milligrams/ kg body weight /day) by different organisations
Allowable Daily Intake
|Allowable Daily Intake of glyphosate (mg/kg BW/day)|
|US Environmental Protection Agency||140|
|European Food Safety Authority||35|
|Environmental working group (EWG)||0.01|
When studying Table 1, the question that comes to mind is why does the allowable daily intake vary so widely between the US EPA and the Environmental Working Group? Different organisations have different attitudes to risk. The EWG effectively have a zero risk for glyphosate because they promote organic food production. Scientific studies show some glyphosate in the diet has no effect on health.
The reader should also note that the market for breakfast cereal is highly competitive and that the EWG is funded by more than 20 companies, many of whom produce organic breakfast cereal.
But wait, there’s more – Natural toxins found in food
While the media has concentrated on agricultural pesticide residues, even organically grown food can contain naturally occurring and highly dangerous toxins . These naturally occurring toxins include:
- mycotoxins – produced by fungi (moulds) – wet harvests, damp storage of foodstuffs
- aquatic biotoxins – produced by algae and dinoflagellates – fish and shellfish
- cyanogenic glycosides – produced by at least 2000 plant species many of which are food crops
- furocoumarins – toxins produced by stress in plants such as parsnips, celery and citrus
- lectins – toxins found in many types of beans which are denatured by soaking then cooking
- solanines and chaconine – found in potatoes, tomatoes and eggplants
- poisonous mushrooms – certain species containing toxins such as muscimol and muscarine
- pyrrolizidine alkaloids – produced by approximately 600 plant species mainly from the families Boraginaceae, Asteraceae and Fabaceae.
Many of these naturally occurring toxins will cause death at higher doses and cancer and organ damage at lower doses. It is important to remember that the dose makes the poison. If you think you have a zero-risk lifestyle you are in for a shock!
So, what does it all mean?
If you want zero agricultural chemicals in your food, eating organically produced foods, might deliver this, but there is no guarantee. Even organically produced foods could contain naturally occurring toxins.
What is certain however is that Australia has world-best regulation and monitoring of chemicals in food and we should feel safe next time we sit down to an Australian grown meal.
Andrew Storrie, AGRONOMO