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Heavy Metal Contaminant Resources

In 2018, the UC Davis California backyard chicken egg study was conducted due to concerns about the potential contamination of eggs by heavy metals in the environment. We used Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to analyze backyard chicken eggs from 344 California residences for the presence of 6 naturally occurring metals. These metals have the potential to affect human health when consumed in excessive amounts.


What do I do if my eggs tested high for one or more metals?

If your eggs tested high for one or more heavy metals, many factors will determine whether you may be affected. These factors include any additional exposures, your level of exposure, the duration of your exposure, and how you become exposed (ex: consumption vs. inhalation). You must also consider any other chemicals you are exposed to, as well as your age, sex, diet, family traits, lifestyle, and state of health. If you are concerned about possible heavy metal exposures, please speak with your physician or health-care provider to discuss testing options and potential health risks with you. Being exposed to these heavy metals or even finding the chemical in your body do not, by themselves, indicate that you have or will have a health problem (ATSDR). 

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What is a "Detection Limit"?

If you received results for the eggs you submitted to our study and they state that the level of a particular metal was "below the detection limit", this simply means that the level that the machine read for your sample was below the minimum concentration at which we can be 99% confident that the measured concentration is distinguishable from a blank sample. A blank sample is one that we know does not contain a detectable amount of the metal of interest.

In other words, we would not be able to say confidently that the concentration of the metal found in your sample was actually detectable by the machine.


What can I do to reduce my chickens’ exposure to heavy metals?

If you live in an urban area, knowing how your land was used previously can help you evaluate potential sources of contamination: was there a gas station next door? A waste site?  This information can help you take precautionary steps. For example, if there was a waste site next door, move your coop to the side of your property furthest from that site and be more diligent about testing soil.

Along those same lines, you want to evaluate chicken areas (coop, runs, free-range areas, etc.) for other potential sources of heavy metals, and/or test these areas for heavy metals. If you are unable to test the soil in these areas, we recommend erring on the side of caution and proceed with proper precautions by assuming the soil may be contaminated. Once potentially contaminated areas are identified, it is your job to prevent your chickens from coming in contact with those areas! You may choose to completely remove access to these areas or add clean cover material (soil, mulch, etc.) to reduce contact with or ingestion of contaminated soil. If you choose to use cover material, remember to inspect the cover regularly and add/maintain material as needed.

To further prevent ingestion of contaminated soil, provide chickens’ regular feed in feeders, and avoid scattering feed, including scratch grains and food scraps, on bare ground. Also, avoid feeding chickens unwashed garden scraps from these areas.

Consider providing a calcium supplement, which may help to reduce the amount of lead that gets into chickens’ eggs.

Please note: if your soil is contaminated, working in the chicken run or backyard soil may result in metal-containing dirt or dust on your clothing. Be sure to change clothes and shower right after working in contaminated soil and avoid spreading dirt from clothes or shoes into your house or car.




How can I test/retest my eggs for heavy metals?

Heavy metal screening can be done at the California Animal Health and Food Safety (CAHFS) laboratory for a fee (phone: 530-752-8700). Because there is currently no published scientific literature on the withdrawal time of heavy metals in chickens and their eggs after ingestion, we recommend retesting your eggs periodically for heavy metals. You may also choose to retest your eggs through the CAHFS laboratory if you submitted eggs to our study and received high results, as there is always a small possibility of laboratory contamination during the process of analyzing samples.




What additional testing can I do to make sure the eggs from my backyard flock are safe?

Chicken Feed Testing: You may also choose to test your chicken feed for heavy metals through the California Animal Health and Food Safety (CAHFS) laboratory for a fee (phone: 530-752-8700).

Soil Testing: High levels of heavy metals in soil may be a risk factor for higher levels of these metals in backyard chicken eggs. To determine whether the environment your chickens live in may be a risk factor contributing to heavy metals in their eggs, you may choose to analyze soil samples from your home. California Environmental Laboratory Accreditation Program (ELAP) accredited laboratories analyze soil samples using approved methods. A map of these laboratories can be found here. ELAP provides evaluation and accreditation of environmental testing laboratories to ensure the quality of analytical data used for regulatory purposes.




What is Arsenic (As) and where does it come from?

Arsenic is a naturally occurring element that can be found in some chicken feed additives, herbal medicines, rice, soil, water, and cigarette smoke, among other sources. While it occurs naturally, arsenic was previously used in pesticides and wood preservatives. The use of arsenic in wood preservatives ended after 2003 but treated wood may still be used in existing structures. It is unknown to what extent this treated wood may contribute to exposure of people to arsenic. There are different forms of arsenic, some of which are not a health concern and others (inorganic arsenic) that are of most concern (ATSDR, Arsenic). Levels of inorganic arsenic in food tends to be relatively low. For more information on arsenic in food, click here.


What do I do if my eggs tested high for Arsenic (As)?

You may choose to speak with your physician or health-care provider about testing for arsenic in your body. There are urine tests available to determine arsenic exposures within the last few days, or hair/fingernail tests to determine arsenic exposures over the past 6-12 months. The results of these tests can show if you have been exposed to arsenic, but it is usually not possible to predict whether you will have any harmful effects unless more is known about when and for how long you were exposed (ATSDR, Arsenic).

Analytical methods used by scientists to determine the levels of arsenic in the environment generally do not determine the specific form of arsenic present. This includes the results from our egg study. Therefore, we do not always know the form of arsenic a person may be exposed to. However, there are several general precautions you can take to reduce you and your chickens’ exposure to arsenic  (ATSDR, Arsenic):

  • If your chicken coop is made from older wood (before 2004) which may have been treated with arsenic, apply a sealant or coating every 1-2 years to prevent direct contact. If your children or chickens have some other access to older wood, consider removing that access or treating that wood as well.
  • Handle arsenic-treated wood with gloves and wash your hands after handling. Have children wash their hands after playing on play structures that could be made of wood that has been treated with arsenic.
  • Never burn or compost wood that has been treated with arsenic. Arsenic-treated wood should never be used as mulch.
  • Arsenic has been found in some drinking water sources in the Central Valley and Southern California. If your water comes from a private well, we recommend having it tested for arsenic. If your water comes from a public water supplier, it will already be tested regularly for arsenic.
    • If the level of arsenic in your drinking water is higher than 10 ppb (parts per billion), use an alternative source of water for drinking and cooking.
    • You may also consider water treatment methods such as reverse osmosis, ultra-filtration, or ion exchange. Boiling or adding chlorine to water will not remove arsenic.
  • Limit contact with soil that has high arsenic levels by using dense groundcover or growing a thick lawn. Pay careful attention to dust and soil control in your home through air filters and frequent cleaning.
  • Because certain additives in chicken feed can contain arsenic, you may also choose to test your chicken feed for heavy metals at the California Animal Health and Food Safety (CAHFS) laboratory for a fee (phone: 530-752-8700), and consider a new diet at the discretion of your veterinarian.

More resources about arsenic:




What is Cadmium (Cd) and where does it come from?

Cadmium is a naturally occurring metal that enters soil, water, and air from mining, industry, and burning coal and household wastes. It can be found in soil, water, tobacco smoke, cheap metal jewelry, rechargeable batteries labeled NiCd or NiCad, and some decorative paints. Cadmium can accumulate in aquatic organisms and agricultural crops. In the United States, the primary source of cadmium exposure for nonsmokers is from the food supply. Generally, leafy vegetables, potatoes, grains, peanuts, soybeans, and sunflower seeds contain high levels of cadmium. Cadmium may also be present in water at elevated levels near cadmium emitting industries (ATSDR, Cadmium).


What do I do if my eggs tested high for Cadmium (Cd)?

You may choose to speak with your physician or health-care provider about testing for cadmium in your body. Urinary cadmium has been shown to accurately reflect the amount of cadmium in the body from recent and past exposure. The amount of cadmium in your blood shows your recent exposure to cadmium.

There are also several steps you can take to reduce your exposure or your body’s absorption of cadmium (ATSDR, Cadmium):

  • Do not smoke tobacco products, as cadmium accumulates in tobacco leaves. The national average blood cadmium level of heavy smokers is more than 4 times greater than the average for non-smokers.
  • Make sure you have a balanced and complete diet. If you do not have enough iron or other nutrients in your diet, you are likely to absorb more cadmium from your food. Your liver and kidneys can change most cadmium to a form that is not harmful, but too much cadmium can overload your system.
  • Dispose of nickel-cadmium batteries properly, and do not allow children to play with batteries.
  • If you work in a cadmium-emitting industry, practice good occupational hygiene by wearing personal protective equipment, washing hands frequently, and showering and changing clothes before returning home, if possible.

 More resources about cadmium:



What is Copper (Cu) and where does it come from?

Copper is a common, naturally occurring metal in rocks, soil, water, sediment, and the air (at low levels). Copper is an essential element for all living organisms, meaning that all plants and animals need some copper in their diet. However, at higher levels, copper can also have some toxic effects. You may be exposed to copper in your water, especially if your water is corrosive and you have copper plumbing and brass water fixtures. Some fungicides used in the garden can also contain copper and lead to increased exposure, especially for hens that forage around those plants or soil. However, your body is generally very good at blocking high levels of copper from entering your bloodstream and you excrete copper through feces and urine (ATSDR, Copper).


What do I do if my eggs tested high for Copper (Cu)?

You may choose to speak with your physician or health-care provider about testing for copper in your body. Testing can show you whether you have been exposed to higher than normal copper levels but cannot be used to predict the extent of exposure or any potential health effects.

There are several steps you can take to reduce you and your chickens’ exposure to copper (ATSDR, Copper):

  • The greatest potential source of copper exposure is through drinking water, so if there is concern about high copper exposure, it is suggested to have your drinking water tested. Drinking water should contain less than 1,300 parts per billion (ppb) of copper. To reduce the amount of copper in your drinking water, it is advisable to run the water for 15-30 seconds before using it, particularly for water that has sat in copper piping or brass faucets overnight.
  • Avoid using garden products that contain high levels of copper, or make sure to wear personal protective equipment and wash hands after. If these products are used, restrict your chickens’ access to the area.


More resources about copper:




What is Lead (Pb) and where does it come from?

Lead is a naturally occurring metal that is used in many industries and products. Most of the high levels found throughout the environment come from human activities. Lead was used in house paint until it was banned in 1978 and in gasoline until it was banned in 1996. Lead solder is no longer used in cans in the United States, so very little lead is found in food nowadays. Lead is fairly widespread in the environment and may be found in a variety of places, including (ASTDR, Lead):

  • Bare soil, peeling paint, and dust in/around homes built before 1978
  • Drinking water in houses containing lead pipes
  • Dust on crops grown in lead-containing soils
  • Near roadways or orchard land where arsenic-containing pesticides have been used
  • Job/Hobby sites such as construction and painting sites, shooting ranges, and recycling facilities for electronics, batteries, and scrap metal
  • Various consumer products

Dr. Birgit Puschner, a veterinary toxicologist, has written a short article titled “A Question of Lead” with additional information on lead exposure and chicken eggs.


What do I do if my eggs tested high for Lead (Pb)?

You may choose to speak with your physician or health-care provider about testing for lead in your body. Blood tests can determine if you have been exposed to lead recently, and x-rays of bones and teeth can show long-term exposures to lead. About 99% of the amount of lead taken into an adult’s body (and only about 32% of the amount taken in by a child) will be excreted within a couple of weeks. Under conditions of continued exposure, not all of the lead that enters the body will be eliminated, leading to potential accumulation of lead in body tissues, especially bone.

To reduce exposure to lead (ASTDR, Lead):

  • Avoid chipped and peeling paint (use a professional service to permanently remove or seal lead-based paint)
  • Cover bare soil near homes built before 1978
  • Use cold water for drinking or cooking to reduce release of lead from some faucets and old pipes. If your pipes contain lead, run water for a while before drinking it so that any lead formed in the pipes can be flushed out.
  • Wash your hands before eating and drinking
  • Eat a well-balanced diet to reduce the amount of lead your body absorbs (adequate calcium, iron, and vitamin C are important for this) and may reduce toxic effects of lead. Experiments have shown that just having food in your stomach greatly decreases the absorption of lead into your bloodstream.
  • Wash fruits and vegetables well, especially if they are grown in soil with high levels of lead.
  • Regularly clean your home of dust and tracked in soil. Having door mats can lower the amount of soil tracked into your home.
  • If you are exposed to lead at work, shower and change your clothes before leaving work, if possible, and bag your work clothes before bringing them into the home.

More resources about lead:


What is the Center for Disease Control's blood reference level for lead?

If you received results for the eggs you submitted to our study, you may have seen us reference the Center for Disease Control (CDC)'s blood reference level for lead. Per the CDC's website, experts now use a reference level of 5 micrograms per deciliter to identify children with blood lead levels that are much higher than most children’s levels. This level is based on the U.S. population of children ages 1-5 years who are in the highest 2.5% of children when tested for lead in their blood.



What is Mercury (Hg) and where does it come from?

Mercury is a naturally found metal that is released into the environment when coal is burned and from past use in gold mines. Metallic mercury is found in fluorescent light bulbs (including compact fluorescent light bulbs) and glass thermometers, among other household and industrial products, but do not pose a risk unless the item is damaged or broken. You may also be exposed to very small amounts of metallic mercury in dental amalgam fillings, but this exposure does not necessarily pose a health risk. Some fungicides and older medicinal products (including laxatives, worming medications, and teething powders) can contain mercury. Because mercury occurs naturally in the environment, everyone is exposed to low levels of mercury in their food, water, and air. These levels are generally considered safe, and nonurban settings generally have even lower background levels of mercury. However, if you are near hazardous waste sites, waste incinerators, or power plants that burn mercury-containing fuels, you may be exposed to metallic mercury vapors. You may be exposed to a form of mercury called methylmercury by consuming fish, shellfish, or marine mammals from mercury-contaminated waters (ASTDR, Mercury). 

Different forms of mercury and types of exposure affect the absorption of mercury in your body. For example, virtually no mercury would be absorbed by your body if you were to swallow small amounts of metallic mercury. Metallic and inorganic mercury that is absorbed into the body leaves primarily in the urine and feces over a period of weeks to months. Methylmercury is the form of mercury most easily absorbed through your gastrointestinal tract and leaves your body slowly over a period of several months after being converted to inorganic mercury by your body.


What do I do if my eggs tested high for Mercury (Hg)?

You may choose to speak with your physician or health-care provider about testing for mercury in your body. There are reliable and accurate ways to measure mercury levels in the body through blood, urine, or hair samples, but most of these tests do NOT determine the form of mercury that you were exposed to. These levels may be used to determine if adverse health effects are likely to occur, especially if results from all three sample types are used. Blood and urine levels are used to determine whether exposure to mercury has occurred and give a rough idea of the extent of exposure, but do not tell exactly how much exposure has occurred. Mercury levels in blood provide useful information about recent exposures to metallic mercury vapor or inorganic forms of mercury (not for methylmercury exposures). Hair can be used to show methylmercury exposures that occurred many months ago).

To reduce your exposure to mercury (ASTDR, Mercury):

  • Properly dispose of and replace older medicinal products containing mercurous chloride (laxatives, worming medications, teething powders) with safer, more effective medicines.
  • Avoid skin-lightening creams containing ammoniated mercuric chloride or mercuric iodide
  • Keep mercury-containing medicines (such as mercurochrome and thimerosal) and non-medicinal products (such as some fungicides and paints) out of reach of children.
  • Use care in handling and disposing of any broken household products and industrial items that contain mercury (such as glass thermometers and fluorescent light bulbs). Call your local health department for advice on this matter.
  • Follow your local Fish and Wildlife Advisories regarding what types and sizes of fish or game are of concern. For California residents, this information can be found here.
  • Avoid allowing your chickens to forage on bare soil (mercury stays on the surface of soil).

If you are concerned about mercury exposure, contact the California Poison Control System hotline at 1-800-222-1222.

More resources about mercury:




What is Nickel (Ni) and where does it come from?

Nickel is a naturally occurring element that is found combined with other elements in all soil, in the earth’s crust, and from volcano eruptions. Most nickel is used to make stainless steel or other metal alloys. Nickel compounds are also used for nickel plating, coloring ceramics, and making some batteries. Food is the major source of exposure to nickel, as nickel occurs at very low levels in the environment and is often attached so strongly to dust or soil particles that it is not easily taken up by plants or animals. Chocolate, soybeans, nuts, and oatmeal are all naturally high in nickel. However, you may also be exposed to nickel by breathing air, drinking water, or smoking tobacco containing nickel. Skin contact with nickel in soil, water, or metals containing nickel can also result in exposure. You may be exposed to higher than average levels of nickel in drinking water if you live near industries that process or use nickel (ASTDR, Nickel).


What do I do if my eggs tested high for Nickel (Ni)?

About 10-20% of the population is sensitive to nickel, but people who are not sensitive to nickel must eat very large amounts of nickel to suffer any harmful health effects. Generally, the level of nickel in foods and drinking water are too low to be of concern, but you may choose to speak with your physician or health-care provider about testing for nickel in your body. Measurements of the amount of nickel in your blood, feces, and urine can be used to estimate your exposure to nickel, but these measurements do not accurately predict potential health effects from exposure to nickel. To reduce your exposure to nickel, limit your intake of high-nickel foods, avoid jewelry containing nickel, and practice good occupational hygiene by wearing personal protective equipment, washing hands frequently, and showering and changing clothes before returning home, if possible (ASTDR, Nickel).

 More resources about nickel:




Where can I get more information about heavy metals?

If you are concerned about possible heavy metal exposures, please speak with your physician or health-care provider. Being exposed to these heavy metals through consumption or even finding the chemical in your body does not, by itself, indicate that you have or will have a health problem.

If you have questions about the results of this study, please contact Dr. Maurice Pitesky at mepitesky@ucdavis.edu or 530-219-1407.

If you have questions or concerns about potential heavy metal contamination or effects of heavy metal contamination, please contact your community or state health or environmental quality department or contact the Agency for Toxic Substances and Disease Registry at cdcinfo@cdc.gov or (770-488-4178).

More information on background levels of heavy metals can be found here.

For more information about the potential health impacts of exposure to heavy metals, visit Biomonitoring California.