This study was conducted by researchers at Emory University, in collaboration with The Organic Center.

About the researchers

Dr. Jean Welsh is a nutritional epidemiologist and an associate professor in Emory University's Department of Pediatrics, School of Medicine with a secondary appoint in the Department of Epidemiology, Rollins School of Public Health. She has over 25 years of experience in public health, with a focus on diet-related risk factors that increase children’ risks of diseases.

Read Dr. Welsh's Bio

Dr. Dana Barr is a Research Professor at Emory University Rollins School of Public Health, and co-director of their Laboratory for Exposure Assessment and Development in Environmental Research. Dr. Barr is the Director of the Analytic Core/Targeted Research Resource of the NIH-funded Human Exposome Research Center: Understanding Lifetime Exposures (HERCULES) and Children's Health Exposure Assessment Resource (CHEAR), respectively. Prior to her position at Emory, she worked for the Center for Disease Control (CDC) for 23 years.

Read Dr. Barr's Bio

Shockingly, the use of sulfamethazine and sulfathiazole for lactating cows has long been banned by the FDA due to concerns about the impact of the drugs on human health.

Sulfa drugs are systemic, which means that once taken, they distribute throughout all body tissues. When cows are treated with sulfonamides, they show up in milk, and studies have suggested that exposure to them could lead to health problems. The biggest health concern for sulfonamide exposure is acute hypersensitivity (a life-threatening allergic reaction). Allergic response rates to sulfonamides are similar to that of penicillin—about 2 percent of the general population are severely allergic to sulfonamides. Outside of allergic reactions, there are many adverse side effects connected to the sulfonamide class of antibiotics from minor ailments like rashes, headaches, vertigo and anemia, to major issues like birth defects (if taken while pregnant), hypothyroidism and thyroid tumors (found in studies on rats).

Sulfonamides are antibiotics that have been prohibited for use in lactating dairy cows since the 1990’s (with the exception of approved use of sulfadimethoxine, sulfabromomethazine, and sulfaethoxypyridazine. Sulfonamides work systemically, which means that once taken, they distribute throughout all body tissues. When cows are treated with sulfonamides, they show up in milk, and studies have suggested that exposure to them could lead to health problems.

Sulfonamides can enter the environment through dust from treated feed, manure and spills from manure lagoons, and water runoff from livestock and poultry operations--which impact aquatic organisms and cause occupational exposure to farmers and farmworkers.

Why should I be concerned about sulfonamides?

1. The biggest health concern for sulfonamide exposure is acute hypersensitivity (life-threatening allergic reaction). Allergic response rates to sulfonamides are similar to that of penicillin--about 2 percent of the general population are severely allergic to sulfonamides.
    
2. Outside of allergic reactions, there are many adverse side effects connected to the  sulfonamide class of antibiotics from minor ailments like rashes, headaches, vertigo and anemia, to major issues like birth defects (if taken while pregnant), hypothyroidism and thyroid tumors in rats.
    
3. Bacterial resistance is a major concern. Sixty to 80 percent of livestock and poultry receive antimicrobials (synthetic antibiotics), and over half of the antibiotics they receive are the same drugs prescribed to humans. This means that when bacterial resistance occurs in animal populations, the resistance also occurs in human populations, causing those shared antibiotics to be ineffective for all animals and humans.

Cross-resistance between sulfonamides is common, meaning that one type of sulfa- antibiotic can lead to bacterial resistance to another sulfa- antibiotic.

4. Sulfonamides for human treatment have largely been replaced by other drugs with less resistance and fewer adverse side effects. However, they are still extensively used in agricultural veterinary medicine and particularly for swine, poultry and cattle. Bacterial resistance emerges gradually, and is widespread in many animal populations. 
    
5. Sulfonamides are routinely detected in soil and water sources, and can be found in other terrestrial and aquatic organisms. 

Sulfathiazole is a synthetic antibiotic that is prohibited from use in lactating dairy cows, and has a detection tolerance limit of zero in milk.

What is it used for?

Sulfathiazole is used in livestock to treat diseases like bovine respiratory disease, bacterial pneumonia, diphtheria, foot rot and postpartum infections. It is also commonly used in powders to treat skin wounds. Sulfathiazole is usually administered orally in various forms including as a mix with feed. While it can be used to treat meat cattle, it cannot be used in lactating dairy cows.

Why is sulfathiazole concerning?

• In general, there are many health issues including severe allergic reactions to the entire sulfa- class of antibiotics (sulfonamides).
• Acute toxicity has been shown in studies on rats and mice
• In humans sulfathiazole has been found to cause skin, eye, and respiratory damage and/or irritation
• Cross-resistance between sulfonamides is common, meaning that one type of sulfa-antibiotic can lead to bacterial resistance to another sulfa- antibiotic.

Sulfamethazine is a synthetic antibiotic with carcinogenic properties and adverse effects including allergic reactions. Sulfamethazine quickly distributes to milk in cows treated with it, so it is prohibited from use in lactating dairy cows, and has a detection tolerance limit of zero in milk to be consumed by humans.

What is it used for?

Historically this antibiotic has been used profusely in swine, chicken and cattle production to treat several diseases and promote fast weight gain, which, in turn, enhanced the success of confined feeding operations, where the closed quarters create an environment susceptible to disease. Today it is still used across many animal production types including fish farms, chickens, swine, cattle, sheep, but is banned for use in lactating cows.

Why is sulfamethazine concerning?

• In general, there are many health issues including severe allergic reactions to the entire sulfa- class of antibiotics (sulfonamides).
• Allergic reactions, jaundice and anemia in exposed infants, and thyroid tumors in rats and mice have been connected to sulfamethazine alone.
• Antibiotic resistance is common across the sulfa- class of antibiotics. The antibiotic itself and sulfamethazine-resistant bacteria have been found in waterways including rivers across the world.

The use of all antibiotics is prohibited in organic dairy production. Not only are antibiotics prohibited for use in organic, but this research shows ZERO incidences of antibiotic residues in organic milk, while 37% of the conventional milk on grocery shelves tested positive for antibiotic residues. To avoid potential contamination by antibiotics you can choose organic milk and dairy products. 

Chlorpyrifos is a widely used organophosphate insecticide that has been used in the U.S. since 1965 in both agricultural and non-agricultural areas. With an estimated 6 million pounds of the chemical used annually on 10 million acres, it has been cited by the EPA as the most commonly used conventional insecticide in the U.S. It has also been shown to have serious health complications for humans who are exposed to it, and it was banned from use in residential areas in 2000, but was still allowed for agricultural use. In 2018, a ban on all uses of chlorpyrifos was court ordered, but it currently remains registered until it undergoes a registration review.

What is Chlorpyrifos used for?

Chlorpyrifos is used to control many different kinds of pests, including termites and mosquitoes in non-agricultural areas (e.g. golf courses), and a variety of agricultural pests including roundworms. It is used in feed and food crop production and in cattle ear tags.

According to the EPA, corn production uses the most chlorpyrifos in terms of total pounds. It is also used on soybeans, fruit and nut trees, vegetable crops like cucumbers and bell peppers, and some fruits including berries.

Direct exposure occurs when spray drift is inhaled or comes in contact with the skin, and indirect exposure occurs when contaminated drinking water and residues on food are ingested.

Why is Chlorpyrifos concerning?

Chlorpyrifos kills insects by interfering with signals in the brain, which causes the nervous system to malfunction. This mode of action occurs in other animals that are exposed, including humans, and children are particularly vulnerable.

Human health: Acute exposure can cause respiratory failure and death. However, exposure to lower doses is associated with multiple health risks that are even more concerning for children. Several studies have linked prenatal exposure to organophosphate pesticides with respiratory and brain development issues as well as autism.

Environmental health: Spray drift can land on nearby plants and soil that other insects and animals eat, and what’s left on the soil can wash away into nearby water sources.  

Chlorpyrifos is toxic to wildlife including fish and aquatic insects, and has been shown to cause reproductive issues in bird and mammals.

Milk is an important source of calcium and other nutrients lacking in the diets of many children. It is also the only beverage, other than water, recommended in U.S. Dietary Guidelines. Milk consumption, however, has been decreasing in the U.S. and recent research suggests that increased concern about industry use of production-enhancing hormones and other chemicals, including pesticides and antibiotics, may be contributing to this trend. The use of these chemicals to produce foods commonly consumed by children is of particular concern. While this study doesn’t touch on how the presence of these chemicals impacts human health, it does show that you can protect yourself from exposure to them by choosing organic. We need more research to determine how chronic, low-level exposure to pesticides affects our health, but until then, if you’re concerned about chemical residues in your milk, this study shows that organic is an easy way to avoid them.

While there are approximately 900 synthetic pesticides approved for use in conventional farming, the National Organic Program only allows about 25 synthetic materials that pose little risk to human health or the environment in organic production. Organic farmers are also allowed to use most naturally derived substances.  However, just because a substance originates in nature does not necessarily mean that it is safe. Thus, natural substances reviewed by the NOSB and found sufficiently harmful to humans and the environment also are prohibited from use in organic farming. All synthetic substances approved for use in organic production and all natural substances prohibited from use in organic production are on the National List of Allowed and Prohibited Substances, which is a component of the organic standards (CFR205.600 – CFR205.606).

Furthermore, when pesticides must be used, organic farmers are encouraged to apply them in a manner that results in the lowest potential exposure risk possible. This can include methods such as pest insect baiting, to lure pests away from crops instead of applying a pest control product directly to the crops, or spot treatments where treatment is strictly consigned to the area on the farm where an infestation or outbreak is actively occurring. As with any farm operation, farmers and farmworkers must adhere to all local and federal labor laws and must apply pest control products according to the label specifications.

The study found no instances of currently used pesticides in organic milk, but the researchers also looked at banned legacy pesticides: pesticides that the US has banned, but stick around in the environment as a pollutant for long periods of time.  DDT and its breakdown metabolite, DDE were used agriculturally on a wide variety of crops as an insecticide, but was banned in 1972. Hexachlorobenzene is a fungicide that was used as a seed treatment, and was banned as part of the Stockholm Convention on Persistent Organic Pollutants, which went into effect in 2004. These pesticides are not currently used in organic or conventional farms, but because of their widespread use in the past, they are still present in the environment. One interesting thing to note is that even these banned chemicals (hexachlorobenzene and DDT’s metabolite DDE) had significantly lower levels in organic milk as compared to conventional milk.  This organic benefit is probably because organic cows are required to have more access to pasture and have more strictly regulated diets (they are primarily grass-fed, and even the feed they do eat is 100% organic).

DDT (dichlorodiphenyltrichloroethane) has been banned for use in the US since 1972. While the chemical elements of DDT are well known for their persistence in the environment, the actual chemical makeup of DDT breaks down quickly into its metabolites, primarily DDE (dichlorodiphenyldichloroethylene), so most evidence of DDT use is currently in the DDE form.  When the study looked at DDE it found that organic milk had significantly lower levels than conventional milk.

Funding for this study came from The Organic Center, which gets its funding from a diversity of sources including federal grants, private foundations, and industry members. However, funders had no influence on the study design or implementation.  Additionally, the lab tests were done blind, meaning that the researchers conducting the laboratory analyses did not know if the samples they were testing were organic or conventional.

This study was published in a peer-reviewed scientific journal that was evaluated by independent, anonymous scientists selected by the journal editors.  The reviewers ensure that the study methods are rigorous and that the study results are sound.

The Organic Center has a strict Conflict of Interest policy, and is committed to communicating and conducting evidence-based, impartial research that safeguards public trust in our work.  They promote objectivity in research by ensuring that the design, implementation, and reporting of research is free of bias. No research or educational activities occurring at, on behalf of, or through the Organic Center will be adversely affected by financial interests of individuals or organizations such as funders, board members, or advisors.