Pesticide residue

Key takeaways

Pesticide residue belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pesticide residue to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pesticide residue from memory before moving on to harder problems.

Reference excerpt

Pesticide residue refers to the pesticides that may remain on or in food, after they are applied to food crops. The maximum allowable levels of these residues in foods are stipulated by regulatory bodies in many countries. Regulations such as pre-harvest intervals also prevent harvest of crop or livestock products if recently treated in order to allow residue concentrations to decrease over time to safe levels before harvest.

Definition

A pesticide is a substance or a mixture of substances used for killing pests: organisms dangerous to cultivated plants or to animals. The term applies to various pesticides such as insecticides, fungicides, herbicides and nematocides. The definition of residue of pesticide according to the World Health Organization (WHO) is: Any specified substances in or on food, agricultural commodities or animal feed resulting from the use of a pesticide. The term includes any derivatives of a pesticide, such as conversion products, metabolites, reaction products and impurities considered to be of toxicological significance. The term “pesticide residue” includes residues from unknown or unavoidable sources (e.g. environmental) as well as known uses of the chemical. The definition of a residue for compliance with maximum residue limits (MRLs) is that combination of the pesticide and its metabolites, derivatives and related compounds to which the MRL applies.

Background Prior to 1940, pesticides consisted of inorganic compounds (copper, arsenic, mercury, and lead) and plant derived products. Most of these were abandoned because they were highly toxic and ineffective. Since World War II pesticides composed of synthetic organic compounds were the most important form of pest control. The growth in these pesticides accelerated in late 1940s after Paul Müller discovered DDT in 1939. The effects of pesticides such as aldrin, dieldrin, endrin, chlordane, parathion, captan and 2,4-D were also found at this time. Those pesticides were widely used due to their effective pest control. Problems with environmental issues of DDT became increasingly apparent, since it is persistent and bioaccumulates in the body and the food chain. In the 1960s, Rachel Carson wrote Silent Spring to illustrate a risk of DDT and how it threatened biodiversity. DDT was banned for agricultural use in 1972 and the others in 2001. Persistent pesticides are no longer used for agriculture, and will not be approved by the authorities. Because the half life in soil is long (for DDT 2–15 years) residues can still be detected in humans at levels 5 to 10 times lower than found in the 1970s.

Regulations Each country adopts their own agricultural policies and Maximum Residue Limits (MRL) and Acceptable Daily Intake (ADI). The level of food additive usage varies by country because forms of agriculture are different in regions according to their geographical or climatical factors. Pre-harvest intervals are also set to require a crop or livestock product not be harvested before a certain period after application in order to allow the pesticide residue to decrease below maximum residue limits or other tolerance levels. Likewise, restricted entry intervals are the amount of time to allow residue concentrations to decrease before a worker can reenter without protective equipment an area where pesticides have been applied.

International Some countries use the International Maximum Residue Limits -Codex Alimentarius to define the residue limits; this was established by Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) in 1963 to develop international food standards, guidelines codes of practices, and recommendation for food safety. Currently the CODEX has 185 Member Countries and 1 member organization (EU). The following is the list of maximum residue limits (MRLs) for spices adopted by the commission.

European Union

The European Union has a searchable database with the Maximum Residue Limits (MRLs) for 716 pesticides. Under the previous system, revised in 2008, certain pesticide residues were regulated by the commission; others were regulated by Member States, and others were not regulated at all.

New Zealand

Food Standards Australia New Zealand develops the standards for levels of pesticide residues in foods through a consultation process. The New Zealand Food Safety Authority publishes the maximum limits of pesticide residues for foods produced in New Zealand.

United Kingdom Monitoring of pesticide residues in the UK began in the 1950s. From 1977 to 2000 the work was carried out by the Working Party on Pesticide Residues (WPPR), until in 2000 the work was taken over by the Pesticide Residue Committee (PRC). The PRC advise the government through the Pesticides Safety Directorate and the Food Standards Agency (FSA).

United States In the US, tolerances for the amount of pesticide residue that may remain on food are set by the EPA, and measures are taken to keep pesticide residues below the tolerances. The US EPA has a web page for the allowable tolerances. In order to assess the risks associated with pesticides on human health, the EPA analyzed individual pesticide active ingredients as well as the common toxic effect that groups of pesticides have, called the cumulative risk assessment. Limits that the EPA sets on pesticides before approving them includes a determination of how often the pesticide should be used and how it should be used, in order to protect the public and the environment. In the US, the Food and Drug Administration (FDA) and USDA also routinely check food for the actual levels of pesticide residues. A US organic food advocacy group, the Environmental Working Group, is known for creating a list of fruits and vegetables referred to as the Dirty Dozen; it lists produce with the highest number of distinct pesticide residues or most samples with residue detected in USDA data. This list is generally considered misleading and lacks scientific credibility because it lists detections without accounting for the risk of the usually small amount of each residue with respect to consumer health. In 2016, over 99% of samples of US produce had no pesticide residue or had residue levels well below the EPA tolerance levels for each pesticide.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Pesticide residue

Start with the simplest possible case. Write down what Pesticide residue claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pesticide residue before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pesticide residue ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pesticide residue

In research: Pesticide residue appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pesticide residue in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pesticide residue is common in secondary-school and first-year university syllabi. It links to neighbouring topics Environmental impact of agriculture, Food and the environment, Food safety, so understanding it makes those chapters shorter.
In everyday life: Look for Pesticide residue outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Pesticide residue in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pesticide residue means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pesticide residue out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pesticide residue in simple terms?

Pesticide residue refers to the pesticides that may remain on or in food, after they are applied to food crops. The maximum allowable levels of these residues in foods are stipulated by regulatory bodies in many countries.

Why does Pesticide residue matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pesticide residue?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pesticide residue.