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Biomarker Wikitext Sep 2024

Definition of Biomarker:
Biomarkers refer to any observable and/or measurable change at the molecular, biochemical, cellular, physiological or behavioral level, which reveals the present or past exposure of an organism to one or more chemical pollutants.[1].
This is the common definition for Biomarker, other definitions can be discussed in the article


Biomarkers provide a measure of the impact of pollutants on organisms exposed over a certain period of time and therefore allow to assess the environmental quality and health status of ecosystems. They are not intended to detect direct lethal effects. Biomarkers can reveal low levels of environmental pollution at an early stage, before it has a negative impact on the entire ecosystem. The predictive power of biomarkers at the ecosystem level is limited by compensatory mechanisms of population response, the complexity of trophic interactions within communities and the complexity of environmental pollution. Therefore, no single biomarker can explain the diversity of pollutants and the multitude of their effects on marine organisms. A set of diverse and coherent indicators via multiple biomarkers is needed to allow systematic screening of different possible effects in response to the different disturbances to which organisms are exposed. Each biomarker then provides a response that correlates with the identified damage, without being influenced by other factors intrinsic to the species, such as seasonal fluctuations, age and sex.[2][3][4][5]

Examples and applications of biomarkers are discussed in the article Common biomarkers for the assessment of marine pollution

Related articles

Biomonitoring of pollution impacts in the marine environment
Bioindicator
Portal:Ecotox


References

  1. ↑ Lagadic, L., Caquet, T. and Amiard, J.C. 1997. Biomarqueurs en écotoxicologie: principes et définitions (introduction). Elsevier Mason SAS, 1997, 2-225-83053-3
  2. ↑ McCarthy, J.F., Jimenez, B.D., Shugart, L.R., Sloop, F.V. and Oikari, A. 1990. Biological markers in animal sentinels: laboratory studies improve interpretation of field data. In: Situ Evaluation of Biological Hazards of Environmental Pollutants. Springer, pp. 163–175
  3. ↑ Beliaeff, B. and Burgeot, T. 2002. Integrated biomarker response: a useful tool for ecological risk assessment. Environ. Toxicol. Chem. An Int. J. 21: 1316–1322
  4. ↑ Galloway, T.S., Brown, R.J., Browne, M.A., Dissanayake, A., Lowe, D., Jones, M.B. and Depledge, M.H. 2004. Ecosystem management bioindicators: the ECOMAN project–a multi-biomarker approach to ecosystem management. Mar. Environ. Res. 58: 233–237
  5. ↑ Chahouri, A., Yacoubi, B., Moukrim, A. and Banaoui, A. 2023. Bivalve molluscs as bioindicators of multiple stressors in the marine environment: Recent advances. Continental Shelf Research 264, 105056
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Biomonitoring of pollution impacts in the marine environment Wikitext Sep 2024


Two approaches can be followed for monitoring the impact of pollutants on marine organisms. One approach is through chemical monitoring, by measuring the presence of pollutants in tissues of exposed organisms by chemical analysis. The second approach is through biomonitoring, by evaluating the response of an organism exposed to a chemical pollutant. This response can be measured through biomarkers at the molecular, biochemical, cellular, physiological or behavioral level. Common biomarkers are described in the article Common biomarkers for the assessment of marine pollution. The organisms that are chosen for biomonitoring are so-called bioindicators. Bioindicators are organisms which are particularly suitable to evaluate the impact of pollutants on marine ecosystems. Biomonitoring complements the information on the health status of the environment provided by the chemical approach.

Response of marine organisms to toxic contaminants

Toxic pollutants (e.g. metals and synthetic chemicals) can accumulate in marine organisms causing wide-ranging physiological effects and eventually threatening both ecology and human health. Organismal stress responses have been observed at different biological levels, such as oxidative damage, activation of antioxidant defenses (cellular level), DNA damage, neurotoxicity (molecular level), impaired filtration or feeding activities, histological damage, growth, development, and reproduction of individuals (physiological level). [1]

During the exposure of an organism to toxic contaminants, the first measurable events take place at the molecular level. As a next step, cells are affected in their integrity, then the tissues and finally the organism as a whole. If exposure to a toxic substance is sufficiently high (by dose or duration of exposure), it can lead to a decrease in the abundance of the exposed species locally, or even to the disappearance of the population. If this species plays an important role in the functioning of the local ecosystem, the entire ecological community may be affected and eventually collapse. It is therefore of great importance to identify in an early stage the impact of a pollutant at the molecular level before possible repercussions on the entire ecosystem. [2] Biomonitoring focuses on the first levels of exposure impact, which can be detected through a range of biomarkers described in the article Common biomarkers for the assessment of marine pollution. Biomonitoring can reveal which are the physiological targets of the toxins, and what is their importance in maintaining the homeostasis of organisms.

The interpretation of biomarkers requires in-depth knowledge of the biotic and abiotic factors of the environment as well as the natural fluctuations of the measured parameter. This knowledge makes it possible to avoid confusion between natural variations, disturbances caused by anthropogenic pollutants and responses to other impacts such as rising oceanic temperatures, changing salinity levels and shifts in nutrient-rich currents, as well as ocean acidification. [2]

Passive sampling: measuring the contaminant exposure

Biomarkers provide an indication of the time-integrated effect of exposure of an organism to pollutants. The interpretation of biomarker observations therefore requires knowledge of the average concentration of pollutants over a certain period. Passive sampling is a technique dedicated to estimating the average concentration of pollutants to which bio-accumulating organisms have been exposed. Passive sampling devices collect pollutants from the environment over a set period of time without the need of external power sources or active sampling procedures. Several devices have been developed capable to collect contaminants such as persistent organic pollutants and heavy metals from the flowing seawater, using sorbent substances with affinity to the targeted contaminants[3].



Biomolecular methods

Biomolecular methods involve the analysis and monitoring of environmental samples using biological molecules (e.g., DNA, RNA, proteins). A recent development is Environmental DNA (eDNA) analysis. By examining DNA fragments shed by organisms into the environment, eDNA analysis enables for the discovery and monitoring of species in their natural habitats using molecular biology techniques. This technique is based on sequencing and analyzing the DNA and comparing the obtained information with existing reference libraries to obtain species identification. It includes shotgun metagenomics (sequencing of all DNA in short fragments), metabarcoding (sequencing a selected gene fragment from a group of organisms such as all fish or bacteria), and quantitative polymerase chain reaction (qPCR). The polymerase chain reaction (PCR) is a common method to make millions to billions of copies of a specific DNA sample rapidly in order to detect and quantify gene expression, using a DNA template. For animals as well as microorganisms, metabarcoding can reveal the presence (or absence), and in some cases relative abundance, of species in a water sample, and qPCR is able in some cases to quantify the number of individuals present or recently present in a given volume of water. Analysis of eDNA enables detection of essentially any organism via trace DNA evidence, assessment of the relative or absolute abundance of particular groups, and precise taxonomic assignment using DNA sequences.[4] The eDNA technique makes it possible to assess the health status of the ecosystem.

The polymerase chain reaction (PCR) can induce PCR bias, resulting in the overestimation of the importance of certain taxa and failure to detect other taxa because they do not amplify. [5]

Metagenomics is a method similar to eDNA that avoids the PCR bias. Metagenomics refers to the study of genetic material extracted directly from an environmental sample, by random sequencing of the entire genomic DNA (the metagenome). Analysis of the metagenome is an efficient method to examine the diversity of microbial communities and their functional capacities. Metagenomics aids in the study of ecosystem dynamics and the assessment of environmental health. It can be utilized for monitoring the environmental conditions to predict disastrous and harmful changes in the environment. A limitation of metagenomics is that a (large) part of the DNA that has been sequenced cannot be reliably assigned taxonomic rank due to a lack of comprehensive reference sequences since, for most species, only small portions of the genome have so far been sequenced. [5]

Related articles

Common biomarkers for the assessment of marine pollution
Bioindicator
Biomarker
Portal:Ecotox


References

  1. ↑ Rochman, C.M., Browne, M.A., Underwood, A.J., Van Franeker, J.A., Thompson, R.C. and Amaral-Zettler, L.A. 2016. The ecological impacts of marine debris: unraveling the demonstrated evidence from what is perceived. Ecology 97: 302–312
  2. ↑ 2.0 2.1 Chahouri, A., Yacoubi, B., Moukrim, A. and Banaoui, A. 2023. Bivalve molluscs as bioindicators of multiple stressors in the marine environment: Recent advances. Continental Shelf Research 264, 105056
  3. ↑ Vrana, B., Allan, I.J., Greenwood, R., Mills, G.A., Dominiak, E., Svensson, K., Knutsson, J. and Morrison, G. 2005. Passive sampling techniques for monitoring pollutants in water. TrAC Trends in Analytical Chemistry 24: 845-868
  4. ↑ Thompson, L.R. and Thielen, P. 2023. Decoding dissolved information: environmental DNA sequencing at global scale to monitor a changing ocean. Current Opinion in Biotechnology 81, 102936
  5. ↑ 5.0 5.1 Serite, C.P., Emami-Khoyi, A., Ntshudisane, O.K., James, N.C., Jansen van Vuuren, B., Bodill, T., Cowley, P.D., Whitfield, A.K. and Teske, P.R. 2023. eDNA metabarcoding vs metagenomics: an assessment of dietary competition in two estuarine pipefishes. Front. Mar. Sci. 10, 1116741
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Bioindicator Wikitext Sep 2024


Definition of Bioindicator:
A bioindicator designates an animal, plant or a group of species, of which some vital functions are modified in response to certain pollutants. These species provide information about the cumulative effects of different pollutants in the ecosystem.
This is the common definition for Bioindicator, other definitions can be discussed in the article

Bioindicators are an early indicator of biotic or abiotic changes in the environment. Bioindicators complement the assessment of pollutant concentrations in water and/or sediment, because the bioindicator organisms only incorporate the bioavailable fraction of polluting substances persisting in its environment. A good bioindicator meets the following requirements: [1][2]

  • sessile or sedentary with a broad spatial and temporal distribution,
  • easy to identify and collect,
  • specific to a particular contaminant or for a class of contaminants,
  • sensitive enough to detect toxicity effects in an early stage preceding the effect at high levels of biological organization,
  • respond in a concentration-dependent manner to change in ambient levels of the contaminant,
  • with small or known variability in response to non-toxicological environmental factors.

Different indicator types can be distinguished: [3] 

* sentinel species : give an indication, by its presence/absence, on the imbalances undergone by the environment,
  • pollution indicator species : have adaptive mechanisms to (certain) pollutants and therefore dominate in the contaminated environment,
  • bioaccumulator species : accumulate xenobiotics either by tissue concentration or by biomagnification through the food chain.

Four levels of bioindicator response to pollution can be observed: [4]

  1. Biointegration: response manifested by the presence of a certain species or by changes in their abundance.
  2. Bioindication : presence of visible alterations at the individual or/and morphological and/or tissue scale.
  3. Biomarker : presence of early infra-individual and invisible reactions, such as cellular or molecular alterations.
  4. Bioaccumulation : the capacity of certain organisms to accumulate environmental pollutants.

Bioaccumulation can occur for pollutants that are not degradable and have a long persistence in marine ecosystems. These pollutants will be ingested by marine organisms, in some cases after being adsorbed to marine particles, such as sediment and plastic debris. Bioaccumulation depends on the liposoluble character and persistence of the molecule in the body. Persistent organic pollutants (POPs) are lipophilic in nature and can easily cross the biological membranes and accumulate in fatty tissues. Bioaccumulation of a pollutant takes place if the rate of intake exceeds the rate of excretion.

Marine bivalves (mussels, oysters, cockles) are the group of marine animals most widely used as bioindicators due to their ability to accumulate contaminants over a relatively long lifespan. Bivalves are fairly resilient to changing environmental conditions and allow for the detection of negative impacts before they become irreversible. [5] Their sessile, burrowing and filter-feeding lifestyle exposes them to a wide range of contaminants, including metals, persistent organic pollutants, pathogens, plastics and environmental changes caused by human activities. They therefore meet many of the requirements to be good bioindicators.


Related articles

Common biomarkers for the assessment of marine pollution
Biomonitoring of pollution impacts in the marine environment
Biomarker
Portal:Ecotox


References

  1. ↑ Kaiser, J. 2001. Bioindicators and biomarkers of environmental pollution and risk assessment. Science Publishers, Enfield.
  2. ↑ Hamza-Chaffai, A. 2014. Usefulness of Bioindicators and Biomarkers in Pollution. International Journal of Biotechnology for Wellness Industries 3: 19-26
  3. ↑ Lagadic, L., Caquet, T. and Amiard, J.C. 1997. Biomarqueurs en écotoxicologie: principes et définitions (introduction). Elsevier Mason SAS, 1997, 2-225-83053-3
  4. ↑ Cuny, D. 2012. La biosurveillance végétale et fongique de la pollution atmosphérique : concepts et applications. Annales Pharmaceutiques Françaises 70: 182-187
  5. ↑ Helmholz, H., Ruhnau, C., Profrock, D., Erbsloh, H.-B. and Prange, A. 2016. Seasonal and annual variations in physiological and biochemical responses from transplanted marine bioindicator species Mytilus spp. during a long term field exposure experiment. Sci. Total Environ. 565: 626–636
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