A bioindicator is a type of living thing, such as a specific animal or group of animals, that can show how healthy or unhealthy an environment is. These living things can reveal changes in their environment through their behavior, numbers, or how they are affected. Many bioindicators are animals, like small water creatures called copepods and other crustaceans found in lakes, rivers, and oceans. Scientists can study these animals for signs of changes in their bodies, how they act, or their behavior, which may show problems in their ecosystem. Bioindicators can help scientists understand how different types of pollution affect an environment over time, something that simple chemical tests cannot do.

A biological monitor, or biomonitor, is a living organism that gives measurable information about the quality of the environment around it. A good biomonitor can show if a pollutant is present and can also help scientists learn how much of the pollutant is there and how strong the exposure was.

A biological indicator is also a method used to check if an environment is free of germs. This process uses special types of microorganisms that are very hard to kill, such as Bacillus or Geobacillus. During this process, these microorganisms are placed in an environment before sterilization. Scientists then test to see if the sterilization process successfully kills them. Because these microorganisms are very hard to kill, if they are destroyed, it means the sterilization process has also likely killed other, less hardy germs in the environment.

Overview

A bioindicator is an organism or a biological response that shows when pollutants are present by showing signs or changes that can be measured. These organisms (or groups of organisms) can provide information about changes in the environment or the amount of pollutants by changing in one of these ways: body changes, chemical changes, or behavior. Scientists can learn this information by studying:

• what elements or chemicals are inside them
• their physical shape or cell structure
• how their bodies process chemicals
• their behavior
• how their populations are organized.

Biomonitors are often better than man-made tools because the best way to know the health of a species or system is to look at the species itself. Bioindicators can show the effects of pollutants on living things when physical or chemical tests cannot. Scientists can check the environment by observing one species instead of the whole group. A small number of indicator species can also help predict how many different types of species are present in an area.

Using a biomonitor is called biological monitoring. This means using the traits of an organism to learn about the environment. Biomonitoring for air pollutants can be done in two ways: passive or active. Passive methods involve observing plants that grow naturally in the area being studied. Active methods use test plants with known reactions and genetic traits placed in the study area.

Biological monitoring refers to measuring certain traits of an organism to learn about the physical and chemical conditions around it.

Bioaccumulative indicators are often used as biomonitors. The type of bioindicator depends on the organism chosen and how it is used.

In most cases, scientists collect baseline data about living conditions in a reference site before starting a study. A reference site should have little or no outside interference, such as human activity, changes in land use, or invasive species. Scientists measure the living conditions of a specific indicator species in both the reference site and the study area over time. Data from the study area is compared to data from the reference site to understand the health of the study area.

A major challenge with bioindicators is that they may not work well in areas with different geography or environments. Because of this, scientists must make sure the methods they use are suitable for the environment they are studying.

Plant and fungal indicators

The presence or absence of certain plants or other living things in an ecosystem can show important information about the environment's health. Scientists use several types of plant bioindicators, such as mosses, lichens, tree bark, bark pockets, tree rings, and leaves. For example, tree bark can absorb pollutants from the air, and scientists can study the bark to find out if pollution is present and how much. Some plants' leaves are harmed by ozone, causing tissue damage, which helps scientists detect this pollutant. These plants are found in areas like the Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayas, southern Asia, and Japan. These regions have many unique species and are especially at risk from ozone pollution, which shows why certain plants are important for checking the environment's health. Scientists use these plant indicators to find out if the environment is changing or being harmed.

Lichens are well-known bioindicators used to check pollution levels. Scientists use scales to measure pollution based on the types of lichen present. One example is the Hawskworth Rose scale. Lichens are useful because different species tolerate different pollutants, so their presence or absence can help scientists understand how much pollution is in the air. For instance, Lobaria pulmonaria is an indicator species used to study the age of forests and the diversity of lichen in Interior Cedar–Hemlock forests in British Columbia. Its presence is linked to higher lichen diversity, showing its value as a bioindicator. Another lichen, Xanthoria parietina, is good at absorbing pollutants like heavy metals and organic compounds. Studies show that X. parietina from industrial areas has more pollutants than those in less polluted areas, proving its usefulness in identifying pollution levels and helping with environmental management.

Fungi are also useful as bioindicators because they are found worldwide and change in response to environmental conditions. Lichens are made of fungi and algae and grow on rocks and trees. They react to changes in forests, such as air quality, climate, and forest structure. If lichens disappear from a forest, it might mean the environment is stressed, such as from high levels of sulfur dioxide or nitrogen oxides. In water systems, the types and amounts of algae can show pollution levels and nutrient levels, like nitrogen and phosphorus. Some genetically modified plants, like grass that changes color when toxins are in the soil, are used as bioindicators.

Penicillium, Aspergillus niger, and Candida albicans are used in the pharmaceutical industry to test for microbes, check product quality, and ensure safety. When used for these purposes, Penicillium and A. niger are standard test organisms. Molds like Trichoderma, Exophiala, Stachybotrys, Aspergillus fumigatus, Aspergillus versicolor, Phialophora, Fusarium, Ulocladium, and certain yeasts are used to check indoor air quality.

Advanced sequencing methods allow scientists to study all the microorganisms in soil or water at once. These methods can use the full community of fungi, called the mycobiome, to check for human-related activities, like sewage or chemical runoff. The types of fungi in an area can show environmental conditions like pH, altitude, and water temperature. Scientists used this method to study 27 streams in Southwestern France.

In another study, scientists sampled fungi in the Augustow Canal in Poland. They measured water quality factors like temperature, oxygen, pH, and levels of nitrogen, carbon, and sulfur. Using microscopic methods and RFLP analysis, they found 38 fungal species, including some that could cause disease. They discovered that the types of fungi helped determine if the water was from a natural or artificial part of the canal. The fungi also helped predict water quality measurements, forming two groups in their analysis.

In another study, scientists used Arbuscular Mycorrhizal Fungi (AMF), which help plants absorb nutrients, to study soil health in Europe. They collected soil samples from different climates and land uses, like farming, grassland, and forests. By analyzing the fungi's DNA, they found eight species that indicated soil pH, eight that showed land use, and two that showed soil carbon levels.

Animal indicators and toxins

Changes in the number of animals, whether more or fewer, can show if pollution is present. For example, if pollution causes a plant to disappear, animals that rely on that plant may have fewer members. In some cases, too many of one species can grow quickly when other species disappear. Stress from pollution can also cause harmful effects in animals, such as changes in their bodies, how they act, or how they feel, even before these issues are seen in the whole population. These early signs can help predict future changes in animal groups.

Pollution and other harmful factors can be studied by looking at different things in animals. Scientists check how much poison is in animal bodies, how often animals have physical problems, how they behave, and how their bodies work.

Amphibians, like frogs and toads, are often used as bioindicators to study pollution. These animals absorb harmful chemicals through their skin and the gills of their young. They struggle to remove certain pesticides from their bodies, allowing these chemicals to build up. Their thin skin makes them especially sensitive to environmental changes, which helps scientists study how pollution affects ecosystems.

Understanding and managing pollution is important for keeping ecosystems healthy. Amphibians are used to study the effects of chemicals like pesticides on the environment. Scientists check how many frogs are in an area, how well they move, and if they have unusual physical features. Fewer frogs or strange body shapes can signal problems like too much sunlight or parasites. Chemicals like glyphosate, used in farming, can harm frogs by entering water systems near where they live.

Frogs that live in ponds are especially sensitive to pollution because they spend time on land and in water during their lives. When they are young, exposure to chemicals often causes changes in their bodies or behavior. These changes can lead to shorter body length, smaller size, or physical problems. These effects increase the risk of death or being eaten by predators.

Crayfish are also studied as bioindicators. For example, scientists look at how much plastic is inside red swamp crayfish to understand pollution from microplastics.

Bats are sensitive to environmental changes and may be useful as bioindicators. Some studies show they can help monitor pollution in rivers, forests, and cities. However, more research is needed, and it can be hard to identify certain bat species or understand what affects their behavior.

Eggs from parasitic worms, called helminths, are used to check if wastewater is safe for reuse. These eggs are the hardest to destroy with common treatment methods and can survive for up to a year in warm climates. They come from worms like roundworms and hookworms. If these eggs are in wastewater and people or animals drink it, they can get sick.

Scientists test samples like dried feces or compost to see if helminth eggs are still alive. The number of roundworm eggs, which are common and easy to spot, is often used to measure how well treatment processes work. Different types of eggs may respond differently to treatments.

Testing methods depend on the sample. For example, sludge is treated with chemicals or heat to reduce the number of eggs. Storing feces for a long time, adding materials like lime, and keeping it warm can also kill the eggs.

Microbial indicators

Certain bacteria can be used as indicator organisms in specific situations, such as when found in water. These indicator bacteria may not cause disease themselves, but their presence in waste can show that other harmful germs might be nearby. Just as there are many types of indicator organisms, there are also many types of indicator bacteria. The most common ones are total coliforms, fecal coliforms, E. coli, and enterococci. The presence of bacteria often found in human waste, called coliform bacteria (such as E. coli), in surface water is a sign of fecal contamination. Pathogens from fecal matter can enter recreational water through ways like sewage, septic systems, urban runoff, coastal waste, and livestock waste.

Because of this, sanitation programs often test water for these bacteria to make sure drinking water systems are not contaminated with feces. Testing methods usually involve taking water samples or passing large amounts of water through a filter to collect bacteria. These samples are then tested to see if bacteria grow on special media, like MacConkey agar. This type of agar only allows certain bacteria to grow, and the way they grow depends on whether they can break down lactose. Another method tests if bacteria use nutrients in ways typical of coliform bacteria.

Indicator bacteria used to show fecal contamination must not stay in the environment for long after leaving the body. Their presence should be closely linked to other fecal germs. Indicator organisms do not need to cause disease.

Non-coliform bacteria, such as Streptococcus bovis and some clostridia, can also be used to show fecal contamination.

Indicator bacteria are measured in many ecosystems and often alongside other tests. In the Great Lakes, a study tested for both fecal indicator bacteria (FIB) levels and pathogen genes. FIB tested included fecal coliforms, E. coli, and enterococci. FIB were collected using methods like membrane filtration and serial dilution, which allowed samples to be tested with PCR to detect pathogen genes. Among 22 locations, 165 samples were analyzed. E. coli levels ranged from less than 2 to 26,000 CFU/100mL, enterococci from less than 2 to 31,000 CFU/100mL, and fecal coliforms from less than 2 to 950 CFU/100mL.

In Malibu, California, the state requires beaches with more than 50,000 visitors yearly to be tested for FIB. High FIB levels, above EPA standards, were found in Malibu Lagoon and other beaches. High FIB levels lead to investigations to find the sources, such as sewage systems, runoff from developments, or wildlife waste. Enterococci levels reached as high as 242,000 MPN/100mL in wastewater systems. Testing FIB helps ensure water safety.

In Texas, FIB levels, especially fecal coliforms and E. coli, were measured in streams near Dallas Fort Worth International Airport. These streams support aquatic life, recreation, and fishing. Standards exist to protect all organisms, including humans. E. coli is used to check if water is unsafe for recreation. If the average E. coli level is over 126 CFU/100mL or more than a quarter of samples exceed 394 CFU/100mL, recreation is considered unsafe. Some sites had E. coli levels above acceptable limits, making them unsuitable for recreation. This shows how testing FIB helps determine water safety for use.

Microorganisms can show the health of aquatic or land ecosystems. They are easier to sample than larger organisms. Some microorganisms produce stress proteins when exposed to pollutants like cadmium or benzene. These proteins can act as early warnings for pollution changes.

Microbial Prospecting for Oil and Gas (MPOG) helps find areas with oil and gas. Oil and gas often seep to the surface through leaks in underground reservoirs. These leaks can change soil chemistry or be detected directly. MPOG methods include DNA analysis, counting microbes in hydrocarbon-based media, or measuring hydrocarbon gas use in cultures.

Microalgae are useful for pollution detection because they are sensitive to pollutants, abundant in nature, and easy to grow. They are important in food webs and have few ethical concerns when used.

Euglena gracilis is a freshwater microorganism that moves using flagella. It is somewhat tolerant of acidic conditions but reacts quickly to pollutants like heavy metals or chemicals. It stops moving or changes direction when exposed to these substances. It is easy to grow, making it useful for testing pollution. One key feature is its gravitactic movement, which helps it sense gravity. Pollutants can damage its ability to sense gravity, causing it to move randomly. This makes it useful for short-term pollution tests. Other organisms, like Paramecium biaurelia, also use gravitactic movement.

Automatic bioassays can use Euglena gracilis to measure its movement in polluted water samples. This helps determine the EC50 (the concentration that affects 50% of organisms) and the G-value (the lowest dilution with no toxic effects).

Macroinvertebrates

Macroinvertebrates are helpful and easy to use for checking how healthy water and land ecosystems are. They are usually present in nature and are simple to collect and identify. This is because most macroinvertebrates can be seen without a magnifying tool, they often have short life cycles (usually lasting one season), and they tend to stay in one place. The type of river and how fast the water flows can influence the kinds of macroinvertebrates found in a river. Different methods and tools are used to study them based on the type of stream and the area it is in. Some benthic macroinvertebrates can survive in polluted water, while others cannot. Changes in the number and types of these creatures in a specific area can show how healthy the water and chemicals in streams and rivers are. Scientists use tolerance levels to study how pollution, like pesticides, or human activities, such as logging or wildfires, affect ecosystems.

Benthic macroinvertebrates live in the bottom areas of streams and rivers. They include aquatic insects, crustaceans, worms, and mollusks that live in the plants and riverbeds. These creatures are found in nearly every stream and river, except in the harshest environments. They can also be found in most stream sizes, except those that dry up quickly. This makes them useful for studies because they are present in areas where larger animals like fish cannot live. Scientists often use benthic macroinvertebrates to measure the health of freshwater streams and rivers. If a stream is considered biologically healthy, it is likely that its water and physical conditions are also good. These creatures are the most common way to test water quality in the United States. While they cannot show the exact causes of problems in rivers, they can help identify common sources of stress.

In Europe, the Water Framework Directive (WFD) started on October 23, 2000. It requires all European Union countries to ensure that all surface and groundwater is in good condition. The WFD also requires countries to monitor the health of biological parts of water systems for specific water types. This led to more use of biological measurements to check river health in Europe. A remote online system was created in 2006 to monitor water quality. It uses bivalve mollusks and sends real-time data between a device in the field (which works for over a year without human help) and a data center. This system connects the behavior of bivalves, like how their shells open, to changes in water quality. It has been used successfully in countries like France, Spain, Norway, Russia, Svalbard, and New Caledonia.

In the United States, the Environmental Protection Agency (EPA) created the Rapid Bioassessment Protocols in 1999. These protocols use macroinvertebrates, along with periphyton and fish, to test water quality.

In South Africa, the Southern African Scoring System (SASS) method uses benthic macroinvertebrates to check water quality in rivers. This method has been improved over 30 years and is now called SASS5, following the ISO/IEC 17025 standard. The SASS5 method is used by South Africa’s Department of Water Affairs to assess river health. This information helps the national River Health Program and the national Rivers Database.

The imposex phenomenon in the dog conch, a type of sea snail, causes females to develop a penis, but it does not make them unable to reproduce. Because of this, the species is used as a sign of pollution from man-made tin compounds in Malaysian ports.