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Endocrine-disrupting chemicals such as estrogenic compounds are found in countless different environments and food products around the world. Acute and chronic exposure of estrogenic chemicals to both humans and animals can result in a myriad of serious health effects. As a result, researchers have developed highly sensitive and accurate biosensors that can detect and measure the presence of estrogens in both the environment and food.
What is Environmental Estrogen?
Environmental estrogen is an endocrine-disrupting chemical (EDC), which, like many other hormone-disrupting contaminants, can interfere with normal hormone metabolic processes in organisms.
Environmental estrogens can be in both natural and synthetic compounds, such as pharmaceutical drugs, pesticides, feed additives, veterinary drugs, phytoestrogens, industrial wastes and certain metals.
Upon interaction with host estrogen receptors, these compounds alter the natural synthesis, secretion, transport, binding, action or elimination of hormones, affecting a cascade of physiological functions.
Natural vs. Synthetic Environmental Estrogens
The main types of naturally produced environmental estrogens include 17b-estrone (E1), estradiol (E2) and estriol (E3).
The primary synthesis sites for these natural estrogens include the ovaries, adrenal glands and adipose tissue of both humans and animals.
Comparatively, the synthetic forms include pharmaceutical drugs such as 17a-ethinylestradiol (EE2) and diethylstilbestrol (DES), which are often used in contraception or hormone therapy.
Several synthetic chemicals can also display estrogenic activity and are environmental estrogens. These chemicals include bisphenol A (BPA), phthalates, alkylphenols (Aps), polycyclic aromatic hydrocarbons (PAHs) and agrochemicals.
BPA, for example, despite being used in the production of plastic and polycarbonate materials, can interact with and block the activity of estrogen receptors, reducing the synthesis of this hormone in the body.
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Effects of Estrogenic Compounds on Environment and Food
Regardless of which type of estrogenic chemical is found in the environment, these substances, depending upon their concentration, can cause harmful effects to exposed organisms.
Within the environment, estrogenic contaminants can be found in groundwater, sediments, residual waters, sewage sludges and even drinking water.
Since marine wildlife are in constant contact with water, these organisms are at the highest risk of suffering from the effects of exposure to estrogenic compounds.
In female fish, for example, exposure to estrogenic compounds effects can result in early vitellogenesis or alterations in the natural plasma levels of vitellogenin, which is a precursor protein in young fish.
Since both male and female fish have estrogen receptors, exposure to estrogen can also lead to unnatural levels of vitellogenin in the male fish. When vitellogenin levels arise in male fish, plasmatic testosterone levels can decline, ovary follicles can develop on their testicles, and pathology of the kidneys and gonads can also be detected.
In addition to the direct health effects that can arise when fish and other marine wildlife are exposed to estrogenic compounds, humans can also experience adverse health effects as a result of consuming fish previously exposed to these chemicals.
How are Environmental Estrogens Detected?
Since there is a wide variety of estrogenic substances that can exist within both the environment and food samples, combined with their wide range of concentrations in each of these sample types, the combination of both chemical and biological assays is often used to monitor environmental estrogens.
Many estrogenic compounds are measured through traditional chemical analytical instruments such as gas chromatography (GC) and GC-mass spectrometry (GC-MS), as well as biological analyses, including enzyme-linked immunosorbent assay (ELISA).
Despite their usefulness, many of these techniques are associated with high operation costs, extensive time requirements, restrictive experimental conditions, and the requirement of well-trained personnel to complete these analyses.
Novel Environmental Estrogen Biosensors
The limitations associated with the traditional instrumental analyses used for environmental estrogen analysis have increased the demand for more convenient and less expensive detection methods.
Some of the different types of biosensors that have been developed for the detection of environmental estrogens include molecule-based, optical, cell-based and model organism-based biosensors.
Molecule-based biosensors
Taken together, molecular biosensors utilize high-affinity molecules such as antibodies and aptamers to recognize target molecules of interest, which, in this case, will be estrogenic compounds.
One of the most reported biosensors used for this application includes electrochemical immunosensors, which are associated with high sensitivity and selectivity, rapid analysis time and simple sample preparation.
To ensure that antibodies are immobilized onto the surface of these sensors, several different novel materials have been tested, some of which include nanocomposites comprised of multi-walled carbon nanotubes (MWCNTs), zinc oxide nanorods and gold nanoparticles coated onto boron-doped diamond-modified electrodes.
Optical biosensors
Both surface plasmon resonance (SPR) and surface-enhanced Raman spectroscopy (SERS) biosensors have been applied to the detection of environmental estrogens.
One recent SPR biosensor used electrostatic suspension immobilization technology to enhance the binding of E2 onto monoclonal antibodies present on the sensor’s interface.
Comparatively, a SERS-based biosensor, which was comprised of aptamer-coated gold/silver core-shell nanoparticles, was recently developed for the quantitative detection of BPA.
Another type of optical biosensor that has demonstrated a high level of specificity includes fluorescent biosensors, particularly those comprised of fluorescent molecules, quantum dots and noble metal nanoparticles.
Cell-based biosensors
Recent advancements in genetic engineering and the replacement of microbial cells with a eukaryotic system have led researchers to incorporate various cell-based biosensors for estrogen detection purposes.
For example, an Escherichia coli molecule was recently engineered to express the estrogen receptor alpha. Upon exposure to estrogenic compounds within different sample types, the bioreceptor reported total estrogenic activity of the tested samples.
Model organism-based biosensors
As compared to cell-based biosensors that are entirely dependent upon in vitro data, several in vivo models have also been proposed for the detection of several different hazardous substances within the environment.
A transgenic line of zebrafish, for example, has been engineered to produce a red fluorescent protein following exposure to different estrogenic substances. Once the researchers collect these fish, fluorescence concentrations are measured and can be used to reflect differences in the levels of these chemicals within a given aqueous environment.
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References and Further Reading
Lu, X., Sun, J., & Sun, X. (2020) Recent advances in biosensors for the detection of estrogens in the environment and food. Trends in Analytical Chemistry 127. doi:10.1016/j.trac.2020.115882.
Pamplona-Silva, M. T., Mazzeo, D. E. C., Bianchi, J., & Marin-Morales, M. A. (2018) Estrogenic Compounds: Chemical Characteristics, Detection Methods, Biological and Environmental Effects. Water Air & Soil Pollution 299(144). doi:10.1007/s11280-018-3796-z.
Ye, Y., Sun, Z., Shen, P., & Sun, X. (2020) Recent advances in electrochemical biosensors for antioxidant analysis in foodstuff. Trends in Analytical Chemistry 122. doi:10.1016/j.trac.2019.115718.
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