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Pesticide Residues in Food


1. Recently, there have been concerns over pesticide tainted vegetables available on the local market.

2. Pesticides are substances used to kill or control unwanted insects, plants, fungi, rodents or other pests. Insecticides, herbicides, rodenticides and fungicides are some commonly used pesticides.

3. Pesticide residue present in food may be resulted from -
‧ direct use of pesticide on the food crop;
‧ animal feeding on pesticide contaminated feed; and
‧ environmental contamination.

Safety and Public Health Significance

1. Depending on the nature of individual pesticide, the amount and duration of exposure, pesticides exceeding safety limits may cause acute and/or chronic effects in humans. Adverse health effects include damage to nervous system or other organs such as the liver and kidneys. Some may be transferred via the placenta or breast feeding, thereby affecting the foetal development.

2. The Joint Food and Agriculture Organization (FAO) and World Health Organization (WHO) Meeting on Pesticide Residues (JMPR)* is responsible for evaluating the safety of pesticide and estimating a safety reference (i.e. Acceptable Daily Intake (ADI)) for individual pesticide based on available toxicological and dietary exposure data.

3. The ADI of a chemical is the estimate of the amount of a substance in food or drinking-water, expressed on a body-weight basis, that can be ingested daily over a lifetime without appreciable health risk to the consumer on the basis of all the known facts at the time of the evaluation.

4. A dietary intake above the ADI does not automatically mean that health is at risk. Transient excursion above the ADI would have no health consequences provided that the average intake over long period is not exceeded as the emphasis of ADI is a lifetime exposure.

Maximum Residue Levels of Pesticides in Food

1. In order to protect the health of the consumer while facilitating international trade, the Codex Alimentarius Commission (Codex) has established Maximum Residue Limits (MRLs) for individual pesticides in selected commodities. MRL is the maximum concentration of a pesticide residue to be permitted in a food commodity. The primary objective of setting MRLs is to protect the health of consumer by ensuring that only the minimum amount of pesticide is applied to food for achieving the actual pest control needs.

2. Codex MRLs are established on the basis of appropriate residue data obtained mainly from supervised field trials. Supervised trials are scientific studies in which pesticides are applied to crops or animals in the way which is intended to reflect commercial practice according to Good Agricultural Practice (GAP). GAP in the use of pesticides includes the authorised safe use of pesticides under actual conditions necessary for effective and reliable pest control and in a manner which leaves a residue which is the smallest amount practicable.

3. Even though the primary purpose of setting MRLs in food is to protect the health of consumers and the levels are intended to be toxicologically acceptable (i.e. do not cause acute or chronic toxicities in humans), it should not be confused with safety limits which are expressed in terms of the Acceptable Daily Intake (ADI, see above) of a particular pesticide residue from all sources. It follows that exposure to pesticide residues in excess of MRLs does not automatically imply a hazard to health. Instead, a residual level exceeding the MRL is more a reflection for non-compliance to GAP.

4. For some pesticides that have been banned or are no longer in use (e.g. DDT, lindane), trace amount of their residues and metabolites may be present in food as environmental contaminants because of their persistence in nature. Codex has established "extraneous maximum residue limits" (EMRLs) for some of these persistent pesticides. EMRL refers to residues of compounds, once used as pesticides but are not any more registered as pesticides, arising from environmental contamination (including former agricultural use of pesticides) or uses of these compounds other than agricultural uses. In another words, the detection of any of these pesticide residues does not necessarily reflect the current use of them in agriculture.

Regulatory Control

1. In Hong Kong, the Centre for Food Safety (CFS) of Food and Environmental Hygiene Department is responsible for the overall safety of food, be it imported or locally produced. The Public Health and Municipal Services Ordinance (Cap. 132) stipulates that no person shall sell or possess or consign to any person for the purpose of selling any food that are unwholesome, adulterated or unfit for human consumption.

2. Under the food surveillance programme of CFS, samples of different foods are taken for analysis and verification if the pesticide residues are within the "tolerance levels". Food containing residues within these levels are considered wholesome and fit for human consumption. Those exceeding the levels reflect deficiency in the practice of application of pesticides or contamination. CFS will take appropriate follow up action to ensure the source farm has rectified the problem.

3. CFS takes reference from the MRLs and EMRLs for pesticides recommended by Codex. Up to date, Codex has set and recommended the MRLs/EMRLs for some 210 pesticides. These maximum limits are revised and published from time to time. Details and latest amendments are available from the Codex's Website (

Advice to the Trade

1. During the use of pesticide for crop protection, the farmers should follow GAP which include but not limited to the following recommendations -

(a) Use only permitted pesticides;
(b) Apply minimum quantities necessary to achieve adequate control;
(c) Leave residues that are the smallest amounts practical and that are toxicologically acceptable;
(d) Unless otherwise specified, the crops should not be harvested for at least 2 weeks after the last treatment; etc.

2. For more information regarding the list of permitted pesticides in Hong Kong as well as the safe use of agricultural pesticides, please visit the Agriculture, Fisheries and Conversation Department's Website at:

Advice to the Public

1. Vegetables are an essential component of a healthy diet. Members of the public are advised to take a balanced diet and eat a variety of fruits and vegetables so as to avoid excessive exposure to contaminants from a small range of food items.

2. To reduce the health risk of pesticide residues due to consumption of pesticide tainted vegetables, members of the public can wash the vegetables well in clean running water for several times, then soak vegetables in water for one hour. Alternatively, they may blanch the vegetables in boiling water for one minute and discard the water used for blanching. The above measures can be adopted together for further risk reduction.

3. For concerned individuals who wish to further reduce their intake of pesticides, they may remove the outer leaves and peel the vegetables.

4. Even though some pesticide residues may be transferred to the infant via human milk, WHO considers that breastfeeding is an unequalled way of providing ideal food for the healthy growth and development of infants; it also contributes to the health and well-beings of mothers.

Risk Assessment Section
Centre for Food Safety
May 2006

* JMPR is the abbreviated title for the Joint Meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Core Assessment Group. The FAO Panel of Experts is responsible for reviewing residue and analytical aspects of the pesticides considered, estimating the maximum residue levels according to supervised trials and GAP. The WHO Core Assessment Group is responsible for reviewing toxicological data on the pesticides, estimating safety reference (i.e. acceptable daily intake) and levels of dietary intakes of pesticide residues. As necessary, acute reference doses for pesticides are estimated along with appropriate estimates of short-term dietary intake.

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