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Defining Biomarkers

Biomarkers are measurable substances or characteristics in the human body that can be used to monitor the presence of a chemical in the body, biological responses, or adverse health effects. The use of biomarkers will help us evaluate potential exposures to pesticides as well as predict effects that may result, allowing us to make decisions that are more protective of human health. Biomarkers are commonly grouped into biomarkers of exposure, effect, and susceptibility. This Web page describes these groups of biomarkers and provides examples.

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Biomarkers of Exposure

Biomarkers of exposure are used to assess the amount of a chemical that is present within the body. Many chemicals can be measured in urine, blood, saliva, and, if they are fat soluble, in body fat and breast milk (e.g., DDT). Biomarkers of exposure provide information on

They may also provide information on the relative importance of different exposure pathways and associated risk. It is important to note that the measurement of a chemical in someone’s body does not by itself mean that chemical has caused adverse health effects.

Additionally, there are a number of uses related to the interpretation of biomarkers of exposure. For example, the measurement of 3-phenoxybenzioc acid (3-PBA) in urine is considered a non-specific biomarker of exposure because 3-PBA is a common metabolite of several pyrethroid pesticides. Therefore, additional information is needed to resolve which pyrethroid was the parent chemical.

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Biomarkers of Exposure Categories

See examples in Table 1

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Biomarkers of Effect

Biomarkers of effect are indicators of a change in biologic function in response to a chemical exposure 1. Thus, they more directly relate to insight into the potential for adverse health effects compared with biomarkers of exposure.

One example of a biomarker of effect is blood cholinesterase, which can become depressed following exposure to organophosphate and N-methyl carbamate pesticides. Measuring cholinesterase levels can be a useful tool for monitoring agricultural workers and identifying workers that may potentially be overexposed to pesticides.

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Biomarkers of Effect Categories

See examples in Table 2

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Biomarkers of Susceptibility

Biomarkers of susceptibility are factors that may make certain individuals more sensitive to chemical exposure. Biomarkers of susceptibility include:

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Table 1: Examples of Biomarkers of Exposure from Different Categories

Exposure Biomarker Category Biological Matrix Example Analytes External stressor
Chemical Breath Styrene (unmetabolized) Styrene
Chemical Feces Bisphenol A (unmetabolized) Bisphenol A
Chemical Serum/Urine 8:2 8:2 DiPap 8:2 8:2 DiPap
Metabolite Blood Styrene Oxide Styrene
Metabolite Urine BPA monoglucuronide Bisphenol A
Metabolite Serum/Urine PFOA 8:2 8:2 DiPap, other fluorinated alkyl acids
Endogenous Surrogate Urine/blood Testosterone Bisphenol A , other endocrine active compounds
Endogenous Surrogate Plasma Butyrylcholinesterase inhibition Toxicity due to acetylcholinesterase inhibition

Table 2: Examples of Biomarkers of Effects from Different Categories

Effect Biomarker Category Biological Matrix Example Analytes Adverse Outcome /Biological Process
Bioindicator Red blood cells Acetylcholinesterase inhibition Toxicity due to acetylcholinesterase inhibition
Bioindicator Blood Maternal T4/T3 Neurological deficiency in offspring
Undetermined Consequence Blood/Urine Malondialdehyde Oxidative stress
Undetermined Consequence Serum/Urine 8-OHdG Oxidative stress
Exogenous Surrogate Blood Lead Neurological deficiency
Exogenous Surrogate Urine 3-PBA Toxicity due to modulation of neuronal sodium channels
Exogenous Surrogate Urine Paranitrophenol Toxicity due to acetylcholinesterase inhibition


3-PBA: 3-phenoxybenzioc acid
8-OHdG: 8-hydroxy-2'-deoxyguanosine
Acetylcholinesterase: AChE
DiPap: Polyfluoroalkyl phosphate ester
PFOA: Perfluorooctanoic acid
T4: thyroxine (a thyroid hormone)

1 Biomarkers of effect correspond to biomarkers as defined by the FDA: Biomarkers Definitions Working Group (2001). Clinical Pharmacology and Therapeutics, 69, p. 89 – 95.

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