Chemical Quality Assurance

Module 4. Environmental contaminants in milk and milk products

Lesson 12
PESTICIDES AND ANTIBIOTICS

12.1 Introduction

Environmental contaminants are chemicals that are present in the environment in which the food is grown, harvested, transported, stored, packaged, processed, and consumed. The physical contact of the food with its environment results in its contamination. These include, Pesticides, Vetrinary drugs, Heavy metals, Radionuclides, Polychlorinated biphenyls, polycyclic aromatic hydrocarbons (PAH) etc. Possible sources of this contamination are

a) Air

Radionuclides (¹³⁷Caesium, ⁹⁰Strontium), polycyclic aromatic hydrocarbons (PAH).

b) Water

Arsenic, mercury.

c) Soil

Cadmium, nitrates, perchlorates. Polychlorinated biphenyls (PCB), pesticides/ insecticides, dioxins, and polybrominated diphenyl ethers (PBDE) are ubiquitous chemicals, which are present in air, water, soil, and the entire biosphere.

d) Packaging materials

Antimony, tin, lead, perfluorooctanoic acid (PFOA), semicarbazide, benzophenone, isopropylthioxanthone (ITX), bisphenol A.

e) Processing/cooking equipment

Copper, or other metal chips, lubricants, cleaning and sanitizing agents.

f) Naturally occurring toxins

Mycotoxins, phytohaemagglutinin, pyrrolizidine alkaloids, grayanotoxin, mushroom toxins, scombrotoxin (histamine), ciguatera, shellfish toxins (see shellfish poisoning), tetrodotoxin, among many others.

12.2 Pesticides

Pesticides are defined as any substance or a mixture of substances used for preventing, destroying, repelling or mitigation of any pest. They are often classified by the type of pest they control e.g. (1) herbicides to protect the plant from weeds; (2) fungicides to suppress the growth of undesired fungi or molds; and (3) insecticides to protect the plants from damage caused by insects. In addition to these main groups, there are acaricides to control mites, nematocides to control worms or nematodes, molluscicides to protect the plant from snails and slugs, rodenticides to control rodents (mice or rats). Pesticides are a key stone components of crop protection. The use of pesticides in food production has provided numerous benefits in terms of increasing production and quality. They are of two types i) Chemical or synthetic organic pesticides and (ii) Biopesticides. Since chemical control of pests is so successful, there has been an explosive expansion in the development of synthetic organic pesticides. Synthetic organic insecticides including mainly, organochloro (OC), organophosphate (OP) and organocarbamate (OCm) pesticides exhibit a high degree of persistence in the environment as compared to the other classes of pesticides. As a result, consumers are exposed to pesticides posing serious threats to public health by entering into the food chain. Mainly through the crop fields, the pesticides have entered into our food chain and are now omnipresent - in air, water, soil, vegetables, fruits, food grains, animal feeds, meat, milk and milk products.

12.2.1 Classification

12.2.1.1 Organochlorine(OC)

Fig. 12.1(a) p, p’ DDT
(Dichlorodiphenyltrichloroethane)



Fig. 12.1 (b) BHC
(Benzene Hexachloride)



Fig. 12.1 (c) Endosulphane

12.2.1.2 Organophosphate (OP)

Fig. 12.2 Malathion

12.2.1.3 Organocarbamate(OCm)

Fig. 12.3 Carbaryl

12.2.2 Source of contamination

12.3 Antibiotics

A drug used to treat infections caused by bacteria and other microorganisms. Originally, an antibiotic was a substance produced by one microorganism that selectively inhibits the growth of another. Synthetic antibiotics, usually chemically related to natural antibiotics, have since been produced that accomplish comparable tasks. Antibiotics are a boon for the maintenance of the health of the cattle as well as human beings. The judicious use of antibiotics has increased the life expectancy of the human beings as well as cattle. However, indiscriminate use of these life saving products i.e. antibiotics has created problems in the dairy as well as food industry due to there residues coming to milk and meat. The presence of antibiotic residues in milk has a great significance to the dairy industry as these residues may lead to inhibited starter activity, inadequate ripening of cheese and affect flavor and texture of milk products. These residues may also affect consumer’s health by causing allergic reactions or by development of resistant microbial strains.

12.3.1 Classification of antibiotics

Antibiotics used in the treatment and management of animals can be chemically grouped in to the following main classes.

A) Aminoglycosides

e.g. Apramycin, gentamicin, lincomycin, streptomycin, neomycin, amikamicin and kanamycin, are having complex but closely related structures. The aminoglycosides are broad-spectrum antibiotics active against both gram-positive and gram-negative organisms but not effective against anaerobes and fungi. They are not well absorbed by alimentary tract or by topical application so they are usually administered intravenously or intramuscularly. This group of antibiotics poses great health hazards, if present in milk and milk products.

Fig. 12.4 Amikacin sulfate

B) β- Lactam compounds

This group consists of natural penicillin and semi-synthetic penicillin and cephalosporins. Penicillins and cephalosporins interfere in the development of bacterial cell wall and are widely used in the treatment of mastitis. After injection of penicillin-G, the milk of the treated animals’ remains contaminated for several days. Cephalosporins are similar to Penicillin in antimicrobial action but less frequently used in veterinary medicine because of its high cost.

Fig. 12.5 General structure of cephlosporine

C) Macrolides

This group consists of a large lactone ring attached with sugar moieties. It includes erythromycin, spiramycin, tylosin, oleandomycin, clindamycin and roxithrocin. The macrolides are active aginst gram-positive bacteria specially staphylococci which are resistant against penicillin. Many times these compounds are also used as growth promoter. They have better tissue penetration ability and frequently used in veterinary medicine.

Fig. 12.6 Macrolides

D) Sulfonamides

Sulfonamides interfere with folic acid synthesis thus inhibiting the bacterial growth. Sulfamethaxazole, Sulfadimidine, sulfamethoxypyridazine, sulfaethoxypyridazine incombination with trimethoprin are commonly used in the treatment. In addition sulfaguanidine and sulfaquinoxaline are also used as feed additive. They are broad spectrum and possess good tissue distribution. They have long half-life and have very good chance of its residues in milk of lactating animals.

Fig. 12.7 Sulfonamides

E) Tetracyclines

Chlortetracycline, oxytetracycline, rolitetracycline, tetracycline, demethylchlortetracycline and doxycycline are the major antibiotics of this group. The structure consisted of basic naphthalene ring and possesses excellent solubility in aqueous medium. These compounds are active against both gram-positive and negative bacteria. However, their systemic absorption in tissues is slower as compared with penicillin, but are well distributed in tissues and less frequently excreted. Their residual occurrence may be more in milk, bones or calcified organs.

Fig. 12.8 Tetracyclines

12.3.2 Important definitions

For better understanding, it is necessary to understand the terminology by regulatory officials. These terms are designed by number of reports of joint meeting of Food and Agriculture Organization (FAO) and World Health Organization (WHO)

12.3.2.1 Residues

Parent compounds or metabolites of drugs/chemicals, having pharmacological action, if persisted in edible products and are likely to harm human health is called as residue. A residue may also occur if drugs or chemicals or added unintentionally in food products. Residue of a drug is expressed in mg/kg or mg/1000ml (ppm) or µg/kg or µg/1000ml (ppb), ng/kg or ng/1000ml (ppt).

12.3.2.2 Unintentional residues

Unintentional residue is that, which occur in feed and food (milk and meat) as a result of circumstances. Such chemicals are never added to protect the food or feed against infection of bacteria, fungus, or parasite. The unintentional residues also include the residue of a drug or chemical that occurs as environmental contaminants. The unintentional residue cannot be differentiated from residue due to actual use of drug or chemicals.

12.3.2.3 Tolerance levels

It is the maximum permissible residual level, which may be present in tissues or milk of animals. A tolerance level is the maximum allowable level of a drug or chemical in feed or food at a specified time of slaughter, milking, processing, storage, marketing and up to time of consumption by human. There are four types of tolerance

1. Finite Tolerance

It is defined as a measurable amount of drug (no-carcinogen) that is permitted in food. For this purpose the acceptable daily intake (ADI) of human is generally determined by applying the safety factor of 1:100. If the drug or chemical is teratogenic (substances or environmental agents which cause the development of abnormal cell masses during fetal growth) the safety factor of 1:1000 is applied.

2. Negligible Tolerance

The toxicologically insignificant amount of residue, resulting in a daily intake of small fraction of maximum ADI is defined as negligible tolerance. Principle for determination of negligible tolerance is similar to that which is used to calculate finite tolerance except that a factor of at least 1:2000 is used and upper allowable limit is imposed.

3. Zero Tolerance

Zero tolerance is determined on the basis of extent of toxicity of drugs/chemicals. For such chemicals no residue is permitted in feed or food because of extreme toxicity in most of the consumers. Zero tolerance is mostly applicable for carcinogenic drugs.

4. Temporary Tolerance

The temporary tolerance is valid only for the restricted period and subjected to revision of availability of experimental data. Generally it is for new drugs and sometime it is also referred as Interim or Administrative tolerance.

12.3.2.4 Withdrawal time

Time required for a drug concentration to fall below the tolerance level is called as withdrawal time. Sometime it is also referred as “Discard Time” or “Withhold Time”. It is expressed in hours, days, weeks or months.

12.3.2.5 Acceptable daily intake (ADI)

The ADI is daily dose of a drug or chemicals residue, which is taken during the entire life-time of a person and appears to be without appreciable risks to health on the basis of all the facts known at that time. ADI value is always subject to revision whenever new information becomes available. It should also be based on the environment and surrounding conditions. It is expressed as mg/kg.

12.3.2.6 Maximum residue limit (MRL)

Maximum concentrations of individual chemicals, or groups of chemicals, especially metabolites, and including pharmaceutical and industrial chemicals, in commodities or tissues to be used as human or animal feeds, and as defined by the food standard codes of a particular country or state; permissible levels vary with local legislation.