How Pollution Impacts Organisms: Assessment Techniques Explained

The impact of pollutants on organisms is assessed through bioindicator species, ecotoxicological experiments, and computer modelling.

Bioindicator species are organisms that are particularly sensitive to changes in their environment and can therefore act as a canary in a coal mine. They include lichens, mosses, and liverworts, which are often used to assess air pollution.

Ecotoxicological experiments are laboratory tests that expose organisms to pollutants under controlled conditions. These can be performed on single species or entire communities, and the results are used to develop guidelines for safe concentrations of pollutants in the environment.

Computer modelling is used to predict how pollutants will affect ecosystems, such as rivers, lakes, and coastal waters. By simulating different physical and chemical conditions, scientists can develop techniques to prevent harmful environmental changes before they occur.

Ecotoxicology

Ecotoxicological experiments are often conducted in laboratories under controlled conditions, providing a guide for comparative assessments. These experiments help understand the relative sensitivity of different species and the toxicity of chemicals. They are designed with strict protocols, including replication, quality control, statistical analyses, and interpretation of results. The experiments aim to maintain consistent chemical concentrations and minimise the accumulation of waste, algae, and other factors that may influence the outcomes. Acute and chronic toxicity tests are performed on various organisms, including fish, invertebrates, birds, and mammals.

The expansion of ecotoxicology has led to the development of species sensitivity distribution (SSD) using toxicity data for a range of species and taxonomic groups, increasing the ecological relevance of laboratory-based toxicity results. Microcosm and mesocosm studies are also used to gain a better understanding of ecological interactions by assessing the effects of contaminants in enclosed experimental ecosystems.

Bioindicators

Biological Indicators

Biological indicators are used to assess the sterility of an environment through the use of highly resistant microorganism strains, such as Bacillus or Geobacillus. These microorganisms are introduced to a given environment before sterilisation, and tests are conducted to measure the effectiveness of the sterilisation processes.

Biological Monitors (Biomonitors)

Biomonitors are organisms that provide quantitative information on the quality of the environment around them. They indicate the presence of a pollutant and can also provide additional information about the amount and intensity of exposure.

Bioaccumulative Indicators

Bioaccumulative indicators are frequently regarded as biomonitors. They respond to the presence of pollutants by changing physiologically, chemically, or behaviourally. These changes can be observed through the study of their content of certain elements or compounds, their morphological or cellular structure, metabolic biochemical processes, or population structure(s).

Types of Bioindicator Species

• Plant and fungal indicators: The presence or absence of certain plant or other vegetative life in an ecosystem can provide important clues about the health of the environment. Examples include mosses, lichens, tree bark, bark pockets, tree rings, and leaves.
• Animal indicators: Changes in animal populations, whether increases or decreases, can indicate pollution. For example, if pollution causes the depletion of a plant, animal species that depend on that plant will experience population decline. Crayfish have also been hypothesised as being suitable bioindicators.
• Microbial indicators: Microorganisms can be used as indicators of aquatic or terrestrial ecosystem health. They are found in large quantities and are easier to sample than other organisms. Some microorganisms will produce new proteins, called stress proteins, when exposed to contaminants such as cadmium and benzene.

Advantages of Bioindicators

• Bioindicators can be employed at a range of scales, from the cellular to the ecosystem level, to evaluate the health of a particular ecosystem.
• They bring together information from the biological, physical, and chemical components of the environment.
• They can be used to assess the cumulative impacts of chemical pollutants and habitat alterations over time.
• They can indicate indirect biotic effects of pollutants when many physical or chemical measurements cannot.
• They are more cost-effective than traditional methods.

Limitations of Bioindicators

• Bioindicators may not be applicable in heterogeneous environments, as it can be difficult to discriminate between natural variability and changes due to human impacts.
• Populations of indicator species may be influenced by factors other than the disturbance or stress being studied.
• The indicator ability of bioindicators is scale-dependent. For example, a large vertebrate indicator may fail to indicate the biodiversity of a local insect community.
• Managing an ecosystem according to the habitat requirements of a particular bioindicator may fail to protect rare species with different requirements.

Computer modelling

To develop models, scientists may concentrate on variables that are the most obvious indicators of nonpoint source pollution and potential eutrophication. For example, in a water body, nitrate-nitrogen levels above 1 part per million (ppm) and total phosphorus levels above 0.1 ppm can contribute to increased plant growth and eutrophication. Similarly, levels of dissolved oxygen below 1 or 2 ppm may indicate that a water body is experiencing eutrophic conditions. At these low levels of oxygen, aquatic organisms may be starved of oxygen and die.

Scientists create a model that simulates these conditions and can then forecast the potential effects of eutrophication, as well as where it might occur. This knowledge helps scientists develop techniques to prevent harmful environmental conditions before they occur.

Research and the use of models provide scientists with important information that they can use to develop long-term monitoring programs. The data gathered from these monitoring efforts is then used to improve the accuracy of the original models.

Laboratory toxicity tests

The choice of test type depends on the specific contaminant and organism under investigation. Standard test methods have been established worldwide, focusing mainly on freshwater temperate species due to the historical recognition of freshwater contamination. However, there is a growing effort to develop toxicity test methods for novel species, especially keystone or foundation species in specific ecosystems, to increase ecological relevance.

The experimental procedures for laboratory toxicity tests are strictly controlled and adhere to protocols for replication, quality control, statistical analysis, and interpretation of results. The tests typically start with a range-finder test to determine a broad range of contaminant concentrations, from no effect to 100% effect. Once the relevant toxicological response is identified, a definitive test is conducted with more precise concentrations.

The duration of the tests is an important consideration, with acute toxicity tests being short-term, typically up to 96 hours, and chronic toxicity tests being longer-term, encompassing a large portion of the organism's lifespan. The choice of duration depends on the organism's lifespan, with some microorganisms doubling their cell number within the acute test timeframe.

The selection of species for toxicity testing is guided by specific criteria, including suitability for laboratory conditions, high reproduction rate, ecological relevance, and quantifiable toxicological responses. However, it is important to acknowledge that rare and endangered species, which may be crucial to protect, are seldom used in these tests.

In conclusion, laboratory toxicity tests are a vital tool for assessing the impact of pollutants on organisms. By following standardised procedures and utilising different test types, scientists can gain insights into the complex relationships between contaminants and various organisms in our environment.

Field studies

In situ studies are the most common approach for examining the potential effects of contaminants on marine communities. These studies are generally focused on macrobenthic communities associated with soft-bottom sediments, as sediments often contain far greater concentrations of contaminants than the water column. Macrobenthos also interact with the sediment via consumption or by residing within it, and therefore may experience multiple exposure pathways.

There are two different approaches most commonly used in in situ community surveys: reference/condition and gradient. The first approach is a comparison of reference and condition sites. The composition of the targeted communities from several relatively unmodified reference sites is compared to those from several sites exposed to the contaminant(s) of interest. Gradient studies, on the other hand, aim to detect variability along a dominant pollution gradient. For example, sites are sampled at increasing distances from the deposition point for deep-sea tailings.

In situ experiments are used to validate correlative studies and to increase our understanding of how contaminants affect marine communities. The two most common approaches are spike and translocation studies. Spiked studies are predominantly sediment-based experiments that involve dosing a sediment with the contaminant of interest. Translocation studies, on the other hand, remove the effect of location by translocating all the sediments to a single location, enabling a direct comparison between sediments obtained from multiple locations.

Laboratory studies are also used to expose whole communities to a contaminant of interest under controlled laboratory conditions. Under such conditions, the physicochemical properties of the water column, as well as the concentration of the stressor, can be controlled. The overlying waters can be continually renewed, ensuring that metabolic waste such as ammonia is removed and not impairing the health of the exposed communities.

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