Fish as Indicators for Environmental Monitoring and Health Risk Assessment Regarding Aquatic Contamination with Pesticides

Contamination of Aquatic Ecosystems with Organic Pollutants-Pesticides

The development of the anthropogenic factor leads to an inevitable disturbance of the balance in aquatic ecosystems. Environmental pollution is the introduction into the environment of new, uncharacteristic substances or exceeding the level of their normal average annual concentration. Water pollutants can also be divided into natural (volcanic eruptions, dead plant or animal remains, etc) or man-made. The latter or chemical contaminants include POPs (persistent organic pollutants) as well as various types of pesticides. POPs are organic substances that have toxic properties; they remain in the environment for a long time; accumulate in the biosphere; they are capable of trans boundary long-range atmospheric transport and deposition; and are likely to have significant negative effects on human health or the environment near and far from their sources.

Pesticides are easily applicable, effective and are a basic practical tool in agriculture and plant protection. By definition, they are poisonous chemicals created by humans to control pests. Based on their chemical nature pesticides are divided into organophosphorus, organochlorine, carbamate, pyrethroid, neonicotinoid and others. Organophosphorous pesticides are one of the most commonly applied, but also dangerous to human health pesticides. They are developed because organochlorine pesticides, such as DDT are already banned. Organophosphorous pesticides have few advantages as they do not accumulate in the environment and have strong insecticidal activity. As a disadvantage we can note their solubility in biological media. In addition, the pesticide is rapidly metabolized in the organism and subsequently transformed into highly toxic metabolites that can damage also the human’s body to varying degrees.

Biological Tools in Environmental Monitoring and Health Risk Assessment

According to De Castilhos Ghisi, [1] it is important to evaluate the effect of pesticides in response to lower trophic levels before they affect higher trophic levels or the entire ecosystem. Changes in the body’s molecular, cellular and tissue levels are used to evaluate the effects of organic pollutants.

Morphological change in cellular and tissue structure is an important parameter. Through the use of morphological methods, the most affected target organs can be identified, and the sensitivity of the organism to the level of toxicity at which it is exposed can be estimated. Histological methods allow differentiation of morphological changes; thus they can be used as tissue-level biomarkers [2]. Furthermore, histochemical techniques help to prove the localization of proteins, lipids, and glycogen at the cellular level; hence the main advantage of applying such techniques is the analysis of biological phenomena in “individual cells”. In addition, the staining intensity can be used to compare proteins, lipids, or glycogen content in liver cells of control groups with experimental groups using different concentrations of toxicants [3].

Peebua, et al. [4] and Costa, et al. [5] propose to use semi-quantitative approaches to determine the extent of histologic changes that enable them to be objectively assessed in order to determine histological changes that have occurred. Moreover, according to Bernet, et al. [2] another criterion for histological studies relates to the actual biological significance of the histological alterations analyzed. This determines the importance of determining histologic changes that are different in different organs.

Biochemical alterations are also considered as reliable biomarkers for assessing aquatic ecosystem pollution. Biochemical changes are an important tool for detecting changes in the metabolism of exposed to pollutants in laboratory or field studies. They are a diagnostic index of the impact of pollutants. Through them, we can detect changes in the levels and activity of enzymes as an indicator of the effects of toxicants. The change in the activity of some antioxidant enzymes depends on the time of exposure, applied concentrations and species. In addition, the change in the enzyme activity can prove oxidative stress, which has been used as a marker in toxicological studies.

Fish as a Major Test Organism in Environmental Monitoring and Health Risk Assessment

Fish are extremely important in aquaculture as major protein source for humans. However, they are also major test organism in the field of aquatic toxicology. The reason for this is that they are very sensitive; they occupy different trophic levels, have large size and can be of different age. In this regards, fish gills are effective bio monitoring tools for investigating the effects of toxicants. They are a multifunctional organ with a large surface area (breathing, ionic regulation, maintenance of acid-base balance and excretion of nitrogen wastes), which is in constant contact with water [6]. Fish liver is another organ, which is studied in terms of aquatic contamination. Its functions are linked with regulation of the metabolism; synthesis of plasma proteins; energy storage in the form of lipids and vitamins, as well as detoxification of different toxicants [7].

Furthermore, changes in the liver enzyme activity levels can be used as reliable biomarkers for contaminated water [8]. In this regards, biochemistry is one of the fastest developing areas in ecological monitoring of aquatic ecosystems.

According to published data from Stoyanova, et al. [9], Yancheva, et al. [10], Stoyanova, et al. [11], the effects of pesticides on fish is expressed on the one hand in changing the histological structure of target organs, such as gills and liver. Histopathological disorders include proliferative and degenerative alterations, as well as those in the circulatory system of the organ. Depending on the concentrations applied and the type of pesticide, these disorders appear to varying degrees. According to the authors, proliferative disorders can be considered as compensatory-adaptive mechanisms that limit the entry of the toxicant. In addition, the authors found that higher concentrations cause degenerative disorders such as necrosis, as well as changes in the organ’s blood system.

In addition, according to Georgieva, et al. [12], Stoyanova, et al. [13], Yancheva, et al. [10] the toxic effect of pesticides also causes changes in the liver morphology. They can be expressed in degenerative disorders such as granular, vacuolar and fatty degeneration, as well as necrosis and necrobiosis. The toxic effect of pesticides also affects the circulatory organ system, which is expressed in hyperemia and lymphocytic proliferation. Moreover, by applying histochemical methods Georgieva, et al. [14], Stoyanova, et al. [15], Yancheva, et al. [16], Stoyanova, et al. [17] found changes in the amount of liver glycogen, as well as a different degree of lipid accumulation in hepatocytes. These alterations prove disturbances in the processes of glycolysis and glyconeogenesis on the one hand, as well as processes of fatty degeneration on the other hand.

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Figure 1: Histological biomarkers in gills of Cyprinus carpio L. under the action of thiamethoxam, H&E [18]. a: Normal histological structure, x200 b: Lamellar lifting at a concentration of 6.6 mg / L thiamethoxam, x400 c: Edema at a concentration of 6.6 mg / L thiamethoxam, 400x d: Proliferation of glandular cells and epithelium at a concentration of 10 mg / L thiamethoxam, x400 e: Fusion of secondary lamellae at a concentration of 20 mg / L thiamethoxam, x400 f: Degeneration of the covering epithelium at a concentration of 10 mg / L thiamethoxam, x400 g: Degeneration of secondary lamellae at a concentration of 10 mg / L thiamethoxam, x400 h: Vasodilation in the secondary lamellae at a concentration of 6.6 mg / L thiamethoxam, x400 i: Vasodilation of the underlying sinus at a concentration of 6.6 mg / L thiamethoxam

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Figure 2: Histological biomarkers in liver of Aristichthys nobilis Rich. under the action of thiamethoxam, H&E [19]. a: Normal histological structure, x200 b: Granular degeneration at a concentration of 6.6 mg / L thiamethoxam, x400 c: Cacuolar and fatty degeneration at a concentration of 10 mg / L thiamethoxam, x400 d: Necrobiotic changes at a concentration of 20 mg / L thiamethoxam, x400 e: Lymphocytic proliferation at a concentration of 20 mg / L thiamethoxam, x400 f: Hyperemia at a concentration of 20 mg / L thiamethoxam, x400