The great majority of residues found in edible tissues of animals have their source at the farm of origin. Most are fairly transient residues derived from recent treatment with pesticides or drugs.
Some, however, are derived from in advertent contamination of soil or buildings with persistent chemicals used in past years. By far the most common cause of residues is the failure to observe the proper withholding period following treatment.
Occasional residues will be acquired during transport, in saleyards, in holding paddocks at abattoirs, or during processing at the abattoir.
Care must be taken to avoid confusion by false positives which can arise from post-sampling contamination or from sample switching. In addition, laboratories must take care to ensure that their standards are accurate and that their calculations are correct.
Logically, the potential for exposure is greatest and the likelihood of residues highest in those areas where farming is more intensive and where chemicals are used more freely.
It can therefore be anticipated that lot-fed animals would be more vulnerable than range-fed animals, that pigs and poultry would be more vulnerable than sheep and cattle, and that dairy cattle would be more vulnerable than beef cattle.
In general, it is found that animals from the tropics are more likely to haveresidues than animals from temperate regions.
At ante mortem inspection any animal showing a diseased condition or showing signs of a recent disease condition should be regarded with suspicion. There is every likelihood that such animals have been recently treated.
There is a particular needfor caution in emergency slaughter. In the normal course of events, there may be little evidence of recent injections but inspectors should nevertheless be watchful.
In the great majority of cases there will be no visual evidence to suggest the presence of residues and laboratory analysis of appropriate samples will be the only means of their recognition.
Control of the Environment
The animal environment will be kept free from contamination if farmers use pesticides in strict accordance with directions on registered labels. This includes compliance with any withholding periods for grazing on treated pastures and crops.
There is little that can be done to overcome contamination resulting from past use of persistent organochlorine pesticides other than to wait for the passage of a sufficient number of years. Present day evaluation procedures should ensure that contamination of the environment is minimal from this time on.
Control of Chemicals
Good regulatory control of pesticides and veterinary drugs is the first line of defense against the occurrence of undesirable residues in agricultural commodities. Control procedures should be designed to ensure that each new product is suitablefor its intended purpose and that it will not give rise to unacceptable residues in food or feed if used in accordance with the directions on the registered label.
There should be legislation to make it an offense to sell or offer for sale any unregistered product. In this way it can be arranged that farmers have access only to approve and properly labeled products. Any residues found in food or feed can then be taken as evidence of misuse.
It does not take many inspectors to maintain surveillance over products on shelves in retail outlets. Effective policing of use on the farm is a far more difficult matter and for this reason many authorities are not convinced of the value of legislation providing power to control use.
Good regulatory control necessitates sound evaluation of data submitted by chemical manufacturers or sponsors. This evaluation can only be performed by knowledgeable persons with sound judgment.
The aim should be to provide the maximum protection for consumers and operators, consistent with keeping producers supplied with the chemical tools they need to remain competitive.
At the same time regulatory authorities must bring forward new products as quickly as possible and avoid putting unnecessary obstacles in the path of manufacturers, who, after all, need some encouragement if they are to keep putting new chemicals into the developmental pipeline.
The system will undoubtedly grind to a halt if regulatory authorities ask for unreasonable safeguards and safety factors.
Standards for Residues
Residues cannot be controlled legally unless legal limits are established. These are called maximum residue limits (MRLs) or tolerances. Food and drug legislation then makes it an offense to sell food in which these limits are exceeded.
It has become accepted procedure that an MRL is set just high enough to cover residues which are difficult to avoid when the particular chemical is used in accordance with good agriculture practice.
This approach derives from the philosophy that notwithstanding the apparent harmlessness of a residue, it is prudent to keep human consumption to the absolute minimum.
This implies that in nearly all cases the MRL is merely a legal limit. Violations are not likely to be a health hazard unless flagrantly excessive.
In any case, the acceptable daily intake (ADI) on which MRLs are based, is estimated as the quantity which would be without observable effect if ingested every day for the whole of a lifetime.
Occasional consumption of food containing levels in excess of the MRL, or even in excess of the ADI, is therefore unlikely to be hazardous.
The second line of defense is surveillance over the occurrence of residues in agricultural commodities. This entails submission of samples for laboratory analysis.
Samples may be collected at random to provide an overall estimate of the occurrence of residues, or taken selectively from areas where use of the particular chemical is greatest, to provide an estimate of residue occurrence in the worst possible situation.
The selective approach is often used in order to make the best possible use of scarce analytical resources. It always seems a little pointless to search for residues in areas where there is little or no likelihood of their occurrence.
Statisticians often criticize analytical programs on the grounds that insufficient numbers of samples are tested. It is noted that 300 consecutive samples must be tested and found compliant in order to be 95% confident that the true violation rate in the population does not exceed 1%.
However, resources do not always permit this luxury and it is often necessary to be satisfied with less.
The Corrective Role
Wherever possible, violative or near violative residues found in a residue survey should be traced back to the farm of origin where suitable corrective action can be taken to ensure there is no recurrence.
Corrective action may vary from advice by extension authorities to quarantine in extreme cases. Quarantine is normally used only in the case of persistent residues.
The effectiveness of trace back depends on identification of the sample. In the case of meat, it depends on animal identification and samples are therefore best taken from the killing floor of an abattoir rather than from a retail meat outlet.
Preparation of Food
Where a residue is removed during normal preparation by peeling or skinning, or if it is destroyed by cooking in a food which is normally cooked, due allowance can be made for this in evaluation of the residue hazard.
Regulatory authorities must watch closely for changes or new trends in agricultural management and practice. Such changes can cause large alterations in the pattern of residues.
Importance of Technological Progress
Farmers must stay abreast of contemporary technology if their product is to be competitive on world markets.
In order that a country’s farmers may have access to new products suited to their unique requirements, it is necessary that the country demonstrate a standard of regulatory control which inspires confidence in their overseas trade partners.
In the absence of an adequate standard of control, considerable caution must be exercised and the approval and adoption of new technology is delayed.
In conclusion, the presence of pesticide residues in feed and animal products is in the focus at the present in the view of WTO. The residues not only affect the public health but also cause economic losses to the livestock industry.
These not only affect the health of livestock and human beings but also affect the quality of animal products. Pesticide residues accumulate in the animals either by direct contact with pesticide or by indirect contact with environment.
Pesticides are used in crops for pest control and they leave the residues in the feed and fodder consumed by animals. The source of contamination of feed and fodder may be by direct spraying or by drift from other crops, contamination of soil and water used for fodder production.
Pesticide use regulations should therefore be emphasized and embraced in order to maintain the minimum residue limits (MRL) in all countries.
The different ways by which pesticide residues reduces the quality and economic value of livestock products; the various was by which pesticide residues gain entry into animal products; and the various ways residues can be managed to keep pesticide residues in the minimum residues limits.