Biological monitoring of water quality

Water quality can be described in terms of physical, chemical and biological characteristics. Bioindicator organisms are those that can be used to identify and quantify the effects of pollutants on the environment. The presence, condition and numbers of certain species of fishes, insects, algae and plants can provide accurate information about the health of a specific river, stream, lake, wetland or estuary. Biological methods are inexpensive and data can be obtained by periodic (e.g.monthly or yearly) visits to the sites. The data is unambiguously related to pollutional impact and scientifically credible. Since pollution is a threat to the biological components of the ecosystem, the assessment of biological variables is the most appropriate. Biological monitoring can indicate past and ongoing pollution events. The reactions of individual organisms, such as behavioural, physiological or morphological changes, can also be studied as responses to pollutant stress. Certain contaminants, particularly metals and organic compounds, may be accumulated in the tissues of organisms. The chemical analysis of the appropriate biological tissues can be used to show that the organism has been exposed to contaminants. The biological approaches can be cheaper than chemical methods in terms of manpower and equipment.

Pros and cons of biomonitoring

Monitoring of biological variables can be cheaper, precise, rapid, easy to perform, require less sophisticated instruments and reflect the integrated expression of pollution load. Biological indicators could identify the possible environmental problems before the health of the aquatic system is seriously altered. Since there is no instrument devised by man to measure toxicity of chemical pollutants, a living organism is a most ‘sensitive sensor’ to evaluate the relative toxicity of pollutants. However the biological approach suffers from the problems posed by the extreme complexity of organisms and ecosystems, endless form of interactions and the non-specific nature of population and community responses.

Biological monitoring is an important tool for water quality management.

Biological monitoring measures the cumulative effect of all the pollutants and overall health of the aquatic ecosystems. Biological can integrate all environmental variables over long periods of time. Generally biological effects occur at concentrations below the analytical capabilities. Toxicity is a property that can be measured only by an organism’s response(Mount,1980).

Definition of biological monitoring

Biomonitoring is the introduction of biological variables for the assessment of the structural and functional aspects of ecosystems. Biological variables are most sensitive to stress which can be easily measured and quantified.A bioindicator is an organism (or community of organisms) that contains information on the quality of the environment. Organisms which are used as indicators of water quality are called sentinel organisms or biological litmus paper or pollution thermometer. The indicator organisms are either plants or animals which show clear symptoms of the possible presence of pollutants. e.g. macroinvertebrates in general( caddis fly larva, may fly larva, stone fly larva etc.), bivalve molluscs (clams, mussels, oysters) and microcrustaceans.

Bioindicators

Indicator organisms may be true indicators or scale indicators.
In true indicators, the degree of pollution- induced damage is related to morphological and/or physical symptoms in one single species.
In scale indicators, the degree of pollutional stress is related to the presence or absence of a sensitive species in a community.
Active bioindication is meant when bioindicators bred in laboratories are exposed in a standardized form in the field for a defined period of time. At the end of the exposure, the reactions provoked in the organisms are analysed.
Passive bioindication organisms already occurring naturally in the ecosystem are examined for their actions.

Biomonitors

A biomonitor is an organism (or community of organisms) that contains information on the quantitative aspects of the quality of the environment.
Accumulation indicators / monitors are organisms that accumulate one or more elements or compounds from their environment. e.g. fresh water mussels.
Effect or impact indicators / monitors are organisms that demonstrate specific or unspecific effects in response to exposure to a certain element or compound or a number of substances.

Criteria for a bioindicator species

1. Highly susceptible to pollutant stress.
2. Widely distributed in many habitats.
3. Taxonomically stable and well known.
4. Low genetic and biological variability
5. Well known natural history with abundant ecological and physiological data .
6. Ready and easy to be sampled, surveyed and manipulated.
7. Economically/ biologically important species.
8. Easily held or cultured in the laboratory for experimental ecotoxicological procedures.

Criteria for selecting a bioindicator species

1.       Relevance – causal relationship to ecologically significant endpoints

2.       Sensitivity – dose responsiveness to specific stressors.

3.       Specificity – responds to specific stressors.

4.       Broad applicability – over temporal and spatial scales.

5.       Representatives – role as surrogate for other responses.

6.       Variability – low variability relative to noise in a ecosystem.

7.       Cost – reasonable for available resources and scope of study.

Benthic macroinvertebrates as good bioindicators

Benthic macroinvertebrates are small animals that live on the bottom of a pond, lake, stream or river for at least part of their lives. E.g. aquatic insects – may flies, damsel flies, dragon flies, stone flies, caddies flies, Dobson flies, true flies and beetles.EPT index is a measure of total number 3 aquatic insect orders such as Ephemeroptera, Placoptera and Trichoptera.

Properties of benthic macroinvertebrates

1.       Live in water for all or most of their life with limited mobility.

2.       Stay in areas suitable for their survival.

3.       Easy to identify, sample or survey

4.       Differ in the range of tolerance to amount and types of pollution.

5.       Are integrators of environmental conditions.

Biomarkers

Biomarkers reflect pollution – induced effects at several levels of biological organization. Biomarkers are measurable biological parameters at the genetic, enzymatic, physiological and morphological levels which indicate qualitative and quantitative aspects of environmental pollution.

Biomarkers can be divided in to markers of exposure and toxic effects.

Biomarkers of exposure represent responses such as induction or inhibition of specific enzymes involved in biotransformation and detoxification as a result of chemical exposure. These biomarkers show early response at the molecular or cellular level and specific in their reaction.

Biomarkers of toxic effects reflect pathological endpoints and are determined at each level of biological organization. These biomarkers serve as integrative markers of complex toxicities and ecologically relevant indicating environmental health at higher levels of biological organization( individual, population, and community level).

Molecular level biomarkers – The activity of cytochrome p 450-dependent monooxygenase system can be analysed as a biomarker of organic chemical pollutant exposure e.g. PCBs, PAHs, dioxins, furans.

Subcellular level biomarkers – the integrity of lysosomal system is analysed to find out the influence of PAHs, heavy metals and organochlorines.

Cellular level biomarkers – the accumulation of neutral lipids in fish hepatocytes is analysed for toxicity induced liver fat metabolism.

Individual level biomarkers – the macrophage aggregate activity is analysed as a marker of pollution induced changes of cellular immune responses.

A biosensor is a measuring device that produces a signal in proportion to the concentration of a xenobiotic substance in a biological system. E.g enzyme, antibody, membrane, organelle, cell, or tissue.

Biological indicators of water quality

Saprobic index(S.I) – a measure of level of organic pollution(Pantle and Buck 1955).

Nyggard’s algal index (Nyggard 1949) and Palmer’s algal index(Palmer 1969) – pollution index using algal species.
Biological index of pollution – BIP
Shannon – Weiner index (Shannon – Weiner 1949)

Potential uses of bioindicators

1. Indicate pollutant exposure

2. Help identify mechanisms of toxicity
3. Provide early warning of impending ecological damage
4. Reveal early indication of environmental recovery or remediation.
5. Important in linking cause/ effect relationship.
6. Can be included in ecological risk assessment.

Ecotoxicological concepts and applications

 The combination of the disciplines ecology and toxicology evolved into another integrative discipline known as ecotoxicology. The science of ecotoxicology is an outgrowth of the link between toxicology, ecology and chemistry. Environmental toxicological studies focus on the nature, properties, effects and detection of toxic substances in the environment and in any environmentally exposed species. The term ecotoxicology was first introduced by Truhaut in 1969 as a natural extension of toxicology. The major difference between toxicology and ecotoxicology is that toxicology deals with the effects of poisons on individual organisms whereas ecotoxicology deals with the effects on population of individuals.

 Aim of ecotoxicology

The aim of ecotoxicology centered on determining the effects of pollutants on the structure and functions of intact ecosystems, communities or assemblages. Ecotoxicologist is one who uses ecological parameters to assess the effects of toxic substances on ecosystems.

Scope of ecotoxicology

- to generate data that will be useful for risk assessment and environmental management.

-to meet legal requirements for regulating the development, manufacture or release of potentially dangerous substances.

- develop empirical or theoretical principles to further understanding of the behavior and effects of chemicals on living systems.

Toxic agent + Environment + host = toxic effects

       Objectives of ecotoxicology

The objective of ecotoxicology is to understand the mechanisms and processes whereby the environmental chemicals exert their effects on ecosystems and their impact on the populations or communities. The purpose of ecotoxicological tests is to predict the response of natural systems using tests in laboratories or model ecosystems. It is therefore an essential tool in the prevention of pollution by supporting environmental policies, laws, standards and control measures.

      

Definitions of ecotoxicology

 Ecotoxicology is a branch of toxicology concerned with the study of toxic effects, caused by natural and synthetic pollutants, to the constituents of ecosystems, animals (including human), vegetables and microbes in an integrated context (Truhaut,1977).

Ecotoxicology is the study of the effects of toxic substances occurring in both natural and man-made environments (Duffus 1980).

Ecotoxicology is the study of the impacts of pollutants upon the structure and function of ecological systems(from molecular to ecosystem) (Landis and Yu1995)

Ecotoxicological tools

Toxicological impacts in the ecosystem can be elucidated through a combination of bioassays using environment/ animal models and long-term field observations. Laboratory bioassays are performed to study feeding, growth, respiration, reproduction, histology, enzyme assays and mortality. Field observations such as tissue concentrations of toxins, species number, species density and population dynamics are crucial. Field experiments like the containment of test organisms at contaminated sites and environmental simulations (microcosms and mesocosms) aid in constructing theoretical models. Modeling throws more insights into our understandings of mechanisms of chemical movements in the environmental compartments.

Toxicological impact on the environment is a four-part process

The release of a chemical into the environment.
The transport of the chemical into biota, with or without chemical/bio-transformation.
The exposure of the chemical to one or more target organisms and
The response of the constituents or whole of the biosphere to the chemical exposure.

The paradigm shift from toxicology to ecotoxicology: Assumptions:

The range of variables that affect population responses is greater than the range that affects individual responses to pollutants.The sublethal effects on individuals may be as important as lethal effects.
 Different individuals of a given species or different populations of the same species may not respond in an identical manner to a pollutant.

Toxic substances have a strong influence both on the ecosystems and on the organisms in the ecosystems. These interactions may be complex and involve a number of parameters or organisms. This may also involve food chains and complex food webs. So there is a great deal of complexity exists because of the great variety of environmental factors and their interactions. The science, techniques and applications of ecotoxicology are evolving rapidly and will continue to contribute more on the understanding of pollution problems.

    Toxicologic principles and laws

Paracelsus (1567) stated “all substances are poisons; there is none which is not a poison. The proper dose separates a poison from a remedy”. Paracelsus is often referred to as the father of toxicology. According to him, the dose makes the poison and the sublethal dose determines the magnitude of the response. There is a threshold concentration for every toxin, which begins to produce effects on organisms; concentrations below this threshold will not have effect.

In order to understand the effects of toxins, Paracelsus believed  the following:

1. It was necessary to use experiments to identify and understand responses to chemicals.
2. There is a difference between toxic and therapeutic properties of chemicals.
3. The dose of a chemical is important in making the distinction between therapeutic and harmful effects and
4. It is possible to identify to some extent, the degree of chemical specificity.

M.J.B.Orfila (1815) described the harmful effects of chemicals on organism. He is often referred to as the founder of toxicology.

  Terminology
A toxic agent is anything that can produce an adverse biological effect. It may be chemical, physical or biological in form.

Chemical agent-e.g. cyanide

Physical agent-e.g. radiation

Biological agent – e.g. snake venom

A toxic substance is simply a material which has toxic properties. It may be a individual toxic chemical or a mixture of chemicals e.g. lead chromate.

It may be organic toxins or inorganic toxins. Organic toxins contain carbon and are man-made large molecules. Inorganic toxins are specific chemicals that are derived from minerals.

Toxic substances may be systemic toxins or organ toxins. A systemic toxin is one that affects the entire body. e.g. potassium cyanide. It affects every cell and organ in the body.

A organ toxin may affect only specific tissues or organs. Lead is a specific organ toxin. It affects 3 target organs namely CNS, kidney and hematopoietic system.

Concept of toxicity – toxicity is usually defined as the inherent property of a chemical to produce adverse biological effects. Toxicity is a function of  concentration (dose) and the duration of exposure. It is characterized in terms of acute or chronic effects and local or systemic effects. Analytical instruments cannot measure toxicity. They can measure the concentration of a chemical in the environment or in organism.

Application of knowledge and techniques of ecotoxicology

1. Determining contaminants leaching from wastes, their critical ecological thresholds and breakpoints.
2. Developing bio-marker –based monitoring systems.
3. Establishing protocols for the protection of natural environment.
4. Developing guidelines for risk assessment of anthropogenic wastes.
5. Contributing remedial ecological restoration measures.