Pesticide contamination of milk and health impact
Definition and types of pesticides
Pesticides are chemical or biological substances used to control, repel, or eliminate harmful organisms. These substances can be classified into several categories based on their target and chemical composition.
Definition of pesticides
Pesticides are defined as chemical or biological agents intended to kill or inhibit harmful organisms, including insects, weeds, fungi, and parasites. They are used in agriculture, forestry, public health, and other sectors to protect crops, stored products, and infrastructure.
Types of pesticides
Pesticides fall into several main categories based on their specific use, with common examples for each:
Insecticides
Insecticides are used to eliminate or control insect pests. They play a vital role in protecting crops and preventing insect-borne diseases. Common examples include DDT, malathion, and permethrin. According to Simpson (2006), insecticides account for about 25% of total pesticide use worldwide.
Herbicides
Herbicides are used to eliminate or inhibit the growth of weeds. They are essential for keeping agricultural fields free of unwanted plants that can compete with crops for nutrients, water, and light. Common examples include glyphosate, atrazine, and dicamba. According to Simpson (2006), herbicides account for the largest proportion of pesticides used, accounting for about 38% of global use.
Fungicides
Fungicides are used to control fungal infections that can harm crops. Their use is particularly crucial in humid regions where fungal diseases are more common. Common examples include mancozeb, chlorothalonil, and myclobutanil. According to Simpson (2006), approximately 10% of pesticides used globally are fungicides.
Rodenticides
Rodenticides are used to eliminate rodents, such as rats and mice, that can damage crops and food stocks. Common examples include bromadiolone and brodifacoum. According to Gheorghe et al. (2017), rodenticides are essential to prevent this damage, but they have a high risk of toxicity.
Nematicides
Nematicides are used to control nematodes, parasitic worms that can damage plant roots and reduce crop yields. Common examples include aldicarb and fenamiphos. According to Jeschke (2017), nematicides are particularly used for crops susceptible to nematode attack, such as vegetables and fruit plants.
Acaricides
Acaricides are used to control mites and ticks, which are harmful to plants and domestic animals. Common examples include abamectin and bifenthrin. According to Jeschke (2017), acaricides are often used in combination with insecticides as part of integrated pest management.
Bactericides
Bactericides are used to eliminate bacteria that cause diseases in plants and animals. Common examples include oxytetracycline and streptomycin. According to Gheorghe et al. (2017), bactericides are essential for the management of bacterial diseases in crops and livestock.
Pesticide use in agriculture
Modern agriculture relies heavily on the use of pesticides to maximize production and protect crops from pests. However, the application of these substances must be carefully managed to minimize negative impacts on the environment and human health.
Modes of application
Pesticides can be applied in a variety of ways depending on the specific needs of the crops, the types of pests to be controlled, and the environmental conditions. Modes of pesticide application include:
Spraying
Spraying is one of the most common application methods, involving the direct application of pesticides to crops using spray equipment. These equipments vary in size and complexity, from hand-held sprayers to sophisticated motorized systems. This application method allows for uniform distribution of the pesticide on the leaves and stems of plants, which is essential for optimum efficacy. Advantages include uniform distribution on plants and the ability to adjust the concentration and volume to meet specific needs. However, spraying also has disadvantages, such as the risk of drift to non-target areas and potential exposure of applicators to the chemicals.
Seed treatment
Seed treatment involves coating seeds with pesticides before planting. This method protects young plants from germination against diseases and soil pests. The treatment may include fungicides, insecticides or a combination of products for integrated protection. Advantages include immediate protection of plants from germination and a reduction in overall pesticide use, since the products are applied directly to the seeds. However, this method requires specialized equipment to coat the seeds and poses a risk of phytotoxicity if the dosage is not correctly calibrated.
Irrigation
The incorporation of pesticides into irrigation systems, called chemigation, allows for uniform distribution of chemicals with the irrigation water. This method is particularly effective for crops that require regular irrigation, allowing both the soil and the aerial parts of the plants to be treated. Its advantages include uniform and efficient distribution, as well as a reduction in the labor required for application. However, it also has disadvantages, such as the risk of contamination of water sources if the systems are not well controlled, and the need for precise management to avoid overdosing.
Aerial
Aerial application uses aircraft or helicopters to spray pesticides over large areas, which is particularly useful for large farms or hard-to-reach areas. This method allows for rapid coverage of large areas and is effective in areas inaccessible by ground equipment. However, it has disadvantages, including a high risk of spray drift and contamination of surrounding areas, as well as high cost and the need for specialist skills to operate the aircraft.
These different modes of application allow the most appropriate method to be chosen based on the specific needs of the crops and environmental conditions, while minimising risks to applicators and the environment.
Factors influencing use
The use of pesticides in agriculture is influenced by various factors. These factors determine the frequency, type and quantity of pesticides needed to effectively protect crops.
Type of crop
Some crops are more vulnerable to pests and diseases than others, thus requiring more intensive use of pesticides.
- Intensive crops: Crops such as fruits and vegetables, which are often grown intensively, may require more pesticide treatments to prevent infestations and diseases.
- Perennial crops: Fruit trees and vineyards may require regular treatments due to their longer growth cycle and prolonged exposure to pests.
Climatic conditions
Climate plays a crucial role in pest and disease dynamics, thus influencing the need for pesticides.
- Temperature and humidity: Hot and humid climates favour the proliferation of insects and fungal diseases, requiring more frequent treatments.
- Precipitation: Rainy periods can increase the risk of fungal diseases, while dry periods can reduce the effectiveness of applied pesticides, requiring reapplications.
Agricultural practices
Crop management methods also influence the need for and effectiveness of pesticides.
- Crop rotation: Alternating crop types from season to season can reduce the buildup of pests specific to a particular crop, thereby decreasing the need for pesticides.
- Intercropping: Planting different crops together can serve as a natural barrier against pests, reducing reliance on pesticides.
- Integrated pest management (IPM) techniques: Using a combination of biological, cultural, and chemical methods to manage pests can reduce the amount of pesticides needed.
Pesticide contamination of milk
Sources of contamination
Pesticide use on forage crops
Pesticides are commonly applied to forage crops such as corn, grass, and soybeans to protect these plants from pests and diseases. These crops are a significant part of the diet of dairy cows. When cows consume these treated plants, pesticide residues can accumulate in their bodies. Over time, these residues can concentrate and be excreted in the milk produced by the cows. This process of bioaccumulation poses a significant risk because even low levels of pesticides in the diet can lead to higher concentrations in milk, especially if exposures are chronic.
Water and soil pollution
Pesticides applied to crops do not always remain confined to the fields. They can enter soils and water sources through rainwater runoff and leaching. Runoff occurs when rainwater or irrigation water carries pesticides from fields to rivers, lakes and groundwater. Leaching occurs when pesticides dissolve in water and percolate through the soil into groundwater.
Cows that drink contaminated water or eat plants grown in contaminated soil can absorb pesticide residues. These residues can then be transferred into the milk produced by the cows. Pesticide contamination of water and soil is a particular concern in areas where pesticide use is intensive and management and control measures are not rigorously implemented.
The two main sources of pesticide contamination of milk are direct application of these products to forage crops and indirect pollution of soil and water sources. These contaminations pose risks to human health and require rigorous prevention and control measures to ensure the safety of milk consumption.
Pesticide contamination process in milk
Transfer of pesticides from cows' feed to milk
Pesticide residues in cows' feed, whether from forage crops or contaminated water, can be absorbed by the cows' digestive system and transferred into their bodies. These residues can then pass into the milk produced by the cows. This bioaccumulation process can increase pesticide concentrations in milk, especially if cows are exposed to pesticides over a long period of time.
Pesticide transfer studies and data
- Transfer of endocrine disrupting compounds: Toxic compounds such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are persistent in the environment and can accumulate in animal feed. One study evaluated the transfer factors of 19 OCPs and 7 PCBs from forage to dairy cows and found residues of these compounds in milk, with transfer factors ranging from 0.03 to 0.28 (Miclean et al., 2012).
- Bioaccumulation of organochlorine pesticides: Another study in Ethiopia showed that residues of organochlorine pesticides, including aldrin, endosulfan and DDT, were present in cow and goat milk, highlighting cross-contamination of fodder crops and water used for animal watering (Deti et al., 2014).
- Fipronil contamination: One study assessed the transfer of fipronil residues from forage to milk. Dairy cows fed fipronil-treated corn silage showed fipronil sulfone residues in their milk, indicating a direct transfer of this pesticide from forage to milk (Le Faouder et al., 2007).
- Correlation between pesticide residues in feed and milk: A study in India found that pesticide residues in feed were correlated with residues in milk. The main contaminants detected were chlorpyrifos, endosulfan, and DDT, with residues sometimes exceeding the maximum permitted levels (Bedi et al., 2018).
- Effect on human health: The transfer of organophosphate and pyrethroid pesticides into milk from cows fed agro-industrial by-products was studied. Residues of these pesticides have been found in amounts sometimes exceeding maximum residue limits, highlighting a potential risk to human health if this milk is consumed (Iftikhar et al., 2014).
These studies show that pesticide residues can be transferred from cows' feed to milk, with important implications for food safety and public health. Continued monitoring and responsible agricultural practices are essential to minimize these risks.
Level of pesticide contamination of milk
Studies conducted in various regions of the world have shown varying levels of pesticide contamination of milk. Here are some examples illustrating this diversity:
- Studies in Europe: Pesticide residues have been detected in milk from some European regions, with variations depending on agricultural practices and the types of pesticides used. For example, a study in Turkey found residues of organochlorine pesticides in cow, buffalo, and sheep milk. Contamination levels varied, with β-HCH concentrations reaching 63.36 ng/ml in buffalo milk, 91.32 ng/ml in cow milk, and 122.98 ng/ml in sheep milk (Bulut et al., 2011).
- Studies in North America: In the United States and Canada, routine monitoring programs have identified pesticide residues in milk, but generally at levels below the maximum residue limits established by the authorities. One study compared organic and conventional milk in the United States and found that current pesticides were detected in several conventional samples (26–60%) but not in organic samples (Welsh et al., 2019).
- Studies in Asia: In some parts of Asia, higher levels of contamination have been reported, often due to intensive pesticide use and less stringent regulations. For example, a study in India found pesticide residues in cow and buffalo milk, with concentrations sometimes exceeding maximum residue limits. Pesticides detected included chlorpyrifos, endosulfan, and lindane (Bedi et al., 2018).
- Studies in Africa: In Egypt, a study showed that residues of organochlorine and organophosphate pesticides in buffalo milk were common, with levels exceeding the tolerated limits for lindane and malathion in 44% of samples (Shaker & Elsharkawy, 2015).
- Studies in South America: In Brazil, an analysis of 132 cow milk samples revealed the presence of HCH (alpha isomer) and endosulfan (alpha and beta isomers), indicating the continued use of these pesticides despite legal restrictions (Ciscato et al., 2002).
These studies highlight the importance of continued monitoring and the application of good agricultural practices to minimize pesticide contamination of milk and protect public health.
Impact on human health
Health effects of pesticides
Acute and chronic toxicity
Pesticide residues can cause acute and chronic toxic effects in consumers of contaminated milk. Acute effects include symptoms such as nausea, vomiting, headaches and dizziness, while chronic effects can lead to long-term damage, including cancer, neurological disorders and reproductive abnormalities (Mansour, 2004).
Effects on the endocrine, immune and nervous systems
Pesticides can disrupt the functioning of the endocrine, immune and nervous systems. For example, some organochlorine and organophosphate pesticides are known to act as endocrine disruptors, affecting the synthesis, function and metabolism of reproductive hormones. They can also cause inhibition of acetylcholinesterase, leading to nervous disorders (Ghuman et al., 2013).
Vulnerable populations
Children and pregnant women
Children and pregnant women are particularly vulnerable to the effects of pesticides due to their rapid development and different metabolism. Pesticide residues in milk consumed by children can pose significant risks to their health, including developmental abnormalities and immune system disorders (de Gavelle et al., 2016).
People with chronic diseases
Individuals with chronic diseases may be more susceptible to the effects of pesticides due to their already compromised health status. The presence of pesticide residues in their diet can aggravate their conditions and increase the risk of further complications (Iftikhar et al., 2014).
Case studies and documented incidents
We present examples of health problems related to the consumption of contaminated milk:
- In India, a study revealed the presence of DDT and HCH residues in milk, exceeding the maximum residue limits (MRLs), leading to risks of cancer and other chronic effects in children who consumed it (Bedi et al., 2015).
- In Egypt, despite the ban on DDT for more than 25 years, persistent residues have been detected in various food samples, including milk, exposing the population to long-term health risks (Mansour, 2004).
- In France, a study on pregnant women showed chronic exposure to several pesticide residues, with cumulative risks to the nervous and thyroid systems (de Gavelle et al., 2016).
These studies highlight the importance of continued monitoring and application of good agricultural practices to minimize pesticide contamination of milk and protect public health.
Regulations and safety standards
International regulations
International regulations regarding pesticide residues in food, including milk, are mainly established by the FAO (Food and Agriculture Organization of the United Nations) and the WHO (World Health Organization) through the Codex Alimentarius. The Codex establishes maximum residue levels (MRLs) for various pesticides to protect consumer health and facilitate international food trade (Ambrus & Yang, 2016).
National regulations
National regulations vary widely across countries regarding pesticide residue limits in milk and other food products.
- United States: Regulations are set by the Environmental Protection Agency (EPA), which sets specific MRLs for each pesticide and food product.
- European Union: The European Food Safety Authority (EFSA) coordinates monitoring and sets harmonized MRLs for member states (EFSA, 2020).
- India: MRLs are set by the Bureau of Indian Standards (BIS) and the Food Safety and Standards Authority of India (FSSAI), with strict monitoring of imported and domestic food products (Khan et al., 2020).
These differences in MRLs across countries can complicate international trade in dairy products, requiring increased harmonization to protect consumer health while facilitating trade (Handford et al., 2015).
Continued monitoring and rigorous enforcement of national and international regulations are essential to ensure the safety of milk and dairy products, minimize risks to public health and facilitate international trade.
VI. Methods for pesticide detection in milk
1) Common analytical techniques
Gas Chromatography (GC)
Gas chromatography (GC) is frequently used to detect pesticide residues in milk. This technique separates the components of a mixture in the gas phase and is often coupled with specific detectors, such as electron capture detector (ECD) or mass spectrometry (GC-MS). For example, one study developed a method to simultaneously determine pyrethroid residues in pasteurized milk using GC-ECD. The recoveries obtained ranged from 82.9% to 109%, with detection limits between 3 and 8.1 ppm (Khay et al., 2009).
High-performance liquid chromatography (HPLC)
High-performance liquid chromatography (HPLC) is another essential technique for analyzing pesticide residues in milk. It uses a liquid phase to separate the components and can be coupled with various types of detectors, such as diode array detector (DAD) or tandem mass spectrometry (LC-MS/MS). For example, a method using HPLC-DAD was developed to detect 30 pesticides in milk, obtaining recoveries ranging from 70% to 100% for the majority of analytes (Rejczak & Tuzimski, 2017).
Innovations and new technologies
QuEChERS extraction
The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method is gaining popularity for the analysis of pesticide residues in milk due to its simplicity and efficiency. This technique consists of solvent extraction followed by dispersive solid phase purification. For example, a recent development of the QuEChERS method allowed the extraction of 41 multiclass pesticide residues in milk, obtaining recoveries ranging from 91.38% to 117.56% (Tripathy et al., 2019).
Enzymatic detection techniques
Enzymatic inhibition-based methods are a rapid and economical alternative for the detection of pesticide residues. These techniques exploit the ability of certain pesticides to inhibit specific enzymes, thus producing a measurable signal. For example, an enzyme inhibition method has been developed to rapidly detect organophosphate and carbamate pesticides in milk, with detection limits ranging from 0.5 to 1.0 mg/kg (Yang et al., 2019).
These advanced detection methods improve the ability to monitor and control pesticide contamination in milk, thereby ensuring food safety and public health.
Prevention and control strategies
Good agricultural practices
Reducing pesticide use
Adopting integrated pest management (IPM) techniques can reduce reliance on chemical pesticides. IPM combines biological, cultural, and mechanical methods to manage pests more sustainably. For example, using crop rotation, biological control with natural predators, and appropriate cultural practices can reduce the need for synthetic pesticides (Eze & Echezona, 2012).
Biological and integrated alternatives
The use of biopesticides, such as plant extracts and biological control agents (insects and microorganisms), is an effective and environmentally friendly alternative to chemical pesticides. These methods are less toxic to humans and the environment, and help prevent pesticide resistance in pests (Lenteren et al., 2018).
Monitoring and quality control
Regular monitoring programs
The establishment of regular monitoring programs allows the detection of pesticide residues in milk and other food products. These programs may include systematic testing of milk samples to verify compliance with maximum residue limits (MRLs) established by national and international regulations (Bedi et al., 2018).
Roles of regulatory agencies
Regulatory agencies play a crucial role in monitoring food safety by establishing standards and guidelines for pesticide use. They are responsible for inspecting farms, verifying compliance with regulations, and implementing corrective measures in case of non-compliance (Jooste & Siebrits, 2004).
Farmer and dairy awareness and training
Farmer training
Training farmers on good agricultural practices and integrated pest management methods is essential to reduce pesticide use and improve food safety. Educational programs can teach farmers how to use pesticides safely and effectively, as well as the benefits of organic alternatives and improved cultural practices (Saikia et al., 2012).
Public awareness
Raising public awareness of the risks of pesticide residues in milk and other food products can encourage increased demand for more sustainably grown products. It can also motivate producers to adopt safer agricultural practices to meet consumer expectations for food safety (Wang et al., 2017).
These combined strategies can help reduce pesticide contamination in milk, thereby improving food safety and public health.
Conclusion
Pesticide contamination of milk is a major food safety and public health concern. Pesticide residues in milk can arise from a variety of sources, including pesticide use on forage crops, water and soil pollution, and transfer of pesticide residues from cows’ feed to milk. The effects of pesticides on human health are diverse and can include acute and chronic toxicities, as well as disruptions to the endocrine, immune, and nervous systems. Children, pregnant women, and people with chronic diseases are particularly vulnerable to these risks. Implementation of good agricultural practices, regular monitoring of pesticide residues, and farmer training are essential to minimize these risks.