Pollutants released into the aquatic environment cause undesirable changes in water quality, and these chemicals, which causes pollution discharged into water resources, can pose significant hazards to the environment and health. One of these chemicals is sodium pyrithione (NaPT).
NaPT (N-hydroxypyridine-2-thione) is a broad-spectrum antimicrobial and fungistatic agent that is the active ingredient in certain anti-dandruff shampoos and are common additive inadhesives, sealants, aerosols, and marine antifouling paints. After it was determined that tributyltin (TBT), which is used as an antifouling, has a toxic effect for the aquatic environment and organisms, pyrithiones were started to be used as antifouling. Copper pyrithione (CuPT), zinc pyrithione (ZnPT), and sodium pyrithione (NaPT) are metallic pyrithions. Although there are many literature studies on the serious toxic effects of CuPT and Zn PT on organisms, there is limited information on the harm of NaPT on living organisms. In these limited studies, NaPT has been found to cause low toxicity in mammals. Although paralysis of the hind limbs is the most typical symptom of intoxication, this effect has not been reported in every experimental animal (Jung et al. 2019). Due to its high cytotoxicity, it has only been used in low concentration in in vitro genotoxicity tests so far.
It has been confirmed that ZnPT causes oxidative stress in both the gills and liver of Gambusia holbrooki and causes specific and irreversible tissue changes (Nunes et al. 2015). Marcheselli et al. (2011) determined that when the sea mussel (Mytilus galloprovincialis) is exposed to sublethal concentrations of ZnPT, adverse effects cause stress in in vivo, and stress causes severe DNA damage in the gills and gastrointestinal gland. They also demonstrated the levels of bioaccumulation after the biocide exposure.
Zhao et al. (2018) found that ZnPT has a broad spectrum of toxicity, causing growth retardation, tissue pathological and physiological changes in the heart, liver, kidney, eye, and bone in zebrafish. In another study, it was found that hindbrain ventricular morphogenesis did not expand as usual at the embryological level (Elsen et al. 2008).
Zhao et al. (2018), an obvious concentration-dependent delay of hatching rate result from ZnPT exposure was detected. Simultaneously, a significant defective development in elongation of the yolk sac and shortening of the entire body length was also observed. Exposure to ZnPT showed inhibitory effects on the pigmentation of zebrafish embryos, possibly due to its inhibitory potential on tyrosinase activity.
NaPT, a pyrithione, is an antimicrobial and antifungal agent widely used in the cosmetics, mining and fuel industries (Dinning et al. 1998). NaPT inhibits substrate transport processes in fungi and bacteria (Chandler and Segel 1978). NaPT is a substance that is easily administered, absorbed from the gastrointestinal tract and intact skin, with known toxicity (Mitoma et al. 1983). After oral administration in rats, rabbits and monkeys, NaPT rapidly absorbed from the gastrointestinal tract and absorption was 88%-100% after oral administration in rats. In studies with mice, 0.15–0.6% of radioactive labelled NaPT was detected in the liver and 0.4–0.8% in other organs after oral or intraperitoneal administration (Ziller 1977; Greim 2012). It has been reported that a single dose of dermal application of radioactive NAPT in rats, it is detected in the muscle and liver close to the application site (Parekh et al. 1970). Because it is cytotoxic, only low concentrations can be tested. In rats, mice, and rabbits given single or multiple doses of NaPT, alternating hind limb paralysis has been reported as a typical manifestation of poisoning. Irreversible eye damage has been seen in species with tapetum lucidum. Since high concentrations are cytotoxic, the genotoxic effect of NaPT tested at low concentrations could not be demonstrated at high concentrations (Greim 2012).
Sublethal concentrations of chemicals can affect important physiological functions such as inhibition of growth, reproduction and biochemical events that may adversely affect the population of the species. Therefore, sublethal toxicity has increasing importance in ecotoxicity testing (Walker 2006).
In the data obtained in this study, mortality rates increased with increasing NaPT concentration and exposure duration. There are limited studies in the literature on the toxic effect of NaPT on fish. However, similar results have been reported in studies on the effects of different toxic substances on different aquatic organisms. Bao et al. (2012), in their study to investigate the toxicity of CuPT and ZnPT on Elasmopus rapax, found the 96 h median lethal concentration (LC50) as 11.5 µg/L and 21.5 µg/L, respectively. Additionally, in a study with Danio rerio zebrafish, the acute toxicity values of ZnPT were found to be LC50 (95% CI) 96 h 0.073 µM (Zhao et al. 2018). Mohamat-Yusuff et al. (2018), investigating the toxicity of CuPT on Japanese medaka fish, found the LC50 96 h value to be 16.58 mg/L. Mochida et al. (2006) found the LC50 for Pagrus major, a teleost for CuPT and ZnPT antifouling, to be 9.3 and 98.2 µg/L, respectively, and 2.5 and 120 µg/L for Heptacarpus futilirostris, a crustacean. Gümüş et al. (2015) found the LC50 48 h value to be 7.32 µg/l for Dreissena polymorpha exposed to CuPT pyrithione.
The ecotoxicity of ZnPT to aquatic test organisms is Lepomis macrochirus 96 h LC50 0.021 mg/l (Madsen et al. 2000), Onchorhynchus mykiss 96 h LC50 0.0032 mg/l (Madsen et al. 2000), Pimephales promelas 96 h LC50 0.0026 mg/l (Madsen et al. 2000), Salvelinus fontinalis 96 h LC50 0.008 mg/l (Madsen et al. 2000), Pagrus major 96 h LC50 0.098 mg/l (Onduka et al. 2010). Additionally, 48 and 72 h LC50 values for the ZnPT invasive species Dreissena polymorpha were found to be 51.9 and 11.5 µg/L, respectively (Yildirim et al., 2015).
In aquatic toxicology, an LC50 of less than 1000 ppb is considered a “very toxic” substance, a substance between 1000 and 10000 ppb is considered a “moderately toxic” substance, and a higher than 10000 ppb is considered a “less toxic” substance. In this study, the LC50 value of NaPT for common carp was determined as 102.7643 µg/L. Therefore, according to this assessment, NaPT is a highly toxic substance for common carp.
Hematological and hormonal parameters are frequently used to reveal the toxic effects of chemicals in a short time. However, studies on the effects of pyrithions such as NaPT, CuPT and ZnPT on hematological and hormonal parameters in fish are not very common in the literature. For this reason, the results of studies on the effects of pyrithiones on these parameters and the effects of other toxic chemicals on these parameters will be more meaningful in the evaluation of the results of this study.
It has been reported that P. olivaceus exposed to ZnPT (10 and/or 50 µg/L) has a decrease in RBC and WBC levels and no significant change in Hb level (Min et al. 2019). Vaiyanan et al. (2015) reported a decrease in Hb level because of the exposure of Cyprinus carpio to monocrotophos pesticide. It was determined that the exposure of Labeo rohita to cypermethrin at sublethal concentration showed a significant decrease in RBC count, Hb amount and hematocrit values compared to the control group (Adhikari et al. 2004). Similarly, Jee et al. (2005) reported that exposure of Korean rockfish (Sebastes schlegelii) to cypermethrin decreased RBC count, Hb level and Hct values. They concluded that these results might be due to the destructive effect of the toxic chemical on the cell membrane. They also suggested that the decrease in RBC count, Hb level and Hct level could cause erythrocyte hemolysis and/or irreparable scars and damage to gill morphology and function. It is also suggested that the decrease in Hb level may be due to the increase in the rate of destruction of hemoglobin or the decrease in the rate of synthesis. Decreases in RBC, Hb, and Hct, which are highly correlated with hematological parameters, have been linked to inhibition of erythropoiesis, red blood cell destruction, hematopoietic tissue destruction in kidney and spleen, and impaired hemopoietic process. A significant increase in the number of WBCs of Cyprinus carpio (Vaiyanan et al. 2015) exposed to monocrotophos and Channa punctatus (Jayaprakash and Shettu 2013) exposed to deltamethrin has been reported. The increase in WBC count has been evaluated as a response to the immune system due to toxic stress. Similar to the above studies, in the present study, NaPT caused decreases in RBC, Hb and HCT values, while it increased WBC count.
It has been determined that 4-nonylphenol reduces the serum IGF-1 level of Atlantic salmon and decreases somatic growth (Arsenault et al. 2004). It has been reported that pesticides induce growth retardation done studies with Oreochromis niloticus, Chrysicthys nigrodigitatus, Clarias gariepinus (Sweilum 2006; Hanson et al. 2007; Bose et al. 2011), Danio rerio (Cook et al. 2005) and Oncorhynchus tshawytscha (Baldwin et al. 2009). In this study, it is assumed that the reason for the decrease in GH and IGF-1 levels is the fact that many toxic substances such as heavy metals and pesticides may inhibit the hypothalamic-pituitary axis.
The results of the current study are similar to the observations of Ajani (2008), who noted that stress causes hormonal changes in fish and impairs its production, and Vijayavel et al.'s (2006) studies where they reported that stressful situation elicits neuroendocrine response in fish.
It has been reported that fish produce an adaptive response to stress by secreting HPI axis hormones (ACTH and cortisol) (Schreck, 1990) and adaptive responses in fish take a very long time (Alexander and Ingram 1992). In studies on most fish species, it has been reported that there is a high increase in plasma cortisol levels in a short time after stress (Barton 2002). It has been reported that cortisol has a significant effect on the dynamics of toxic substances in fish (Mommsen et al. 1999) and intended to meet the increased energy needs of animals when faced with stress (Barton 2002; Langiano and Martinez 2008). It has been reported in studies that fish increase the plasma glucose level as a very common response under stress conditions and this is aimed at meeting the increased energy demand of tissues such as the brain, gill and muscle (Barton 2002), and cortisol mediates the hyperglycemic response in many teleost species (Wendelaar Bonga 1997). Studies have reported that the inhibition of ACh receptors affects the release of ACTH (Hontela 2005; Aluru and Vijayan 2006). This study also suggests that the increase in ACTH and cortisol levels activates the HPI axis adaptively to overcome stress by eliminating the neurotoxic effect.
Fish endocrine responses can also be considered as early warning indicators to assess the response to toxic stress and pollution (Hontela et al. 1993). Additionally, the measurement of circulating hormone levels can provide additional information on the lethal effects of chemicals (Folmar et al. 1993). Thyroid hormones (THs) are expressed in neuroendocrine activation of the hypothalamic-pituitary-thyroid axis (Eales 2006; Zoeller et al. 2007) and are active in almost all vertebrate cells (Heijlen et al. 2013). The thyroid gland is responsible for the secretion of thyroid hormones, which regulate growth, development and basal metabolism. It is also responsible for the secretion of calcitonin, which regulates calcium homeostasis. Many environmental pollutants negatively affect thyroid function and development (Li et al. 2008; He et al. 2012; Katuli et al. 2014; Naderi et al. 2014, 2015). Hypothalamic-pituitary-thyrotropin (HPT) hormones play an important role in growth metabolism in fish due to their effects on energy metabolism, lipid metabolism (Leatherland 1994; Lynshiang and Gupta 2000; Eales 2006; Blanton and Specker 2007) and genetic transcription (Zoeller et al. 2002; Li et al. 2009; Liu et al. 2011). Serum TSH, T3 and T4 levels are widely used as reliable indicators of thyroid function in experimental animals, and changes in serum concentrations of these hormones may reflect impaired synthesis and secretion in peripheral metabolism (Kelly 2000; Yousif and Ahmed 2009). Tagawa and Hirano (1991) reported that the partial reduction of T3 and T4 hormones in Oryzias latipes fish species has a significant effect on hatchability, survival and development of young fish. Additionally, studies have shown that the inhibition of the thyroid gland prevents metamorphosis in larvae and juvenile fish (Miwa and Inui 1987), while exogenous T3 and T4 administration causes early metamorphosis in fish (Brown 1997).
Similar to the results of this study, they reported increased TSH levels in Liza aurata (Oliveira et al. 2011) collected from contaminated areas, and Danio rerio exposed to triadimefon (Liu et al. 2011) and perchlorate (Patiño et al. 2003). Similar to this study, Yu et al. (2013) reported a significant decrease in T4 levels in zebrafish exposed to hexaconazole and tebuconazole fungicides. Also, Coimbra et al. (2005) stated that endosulfan exposure on Nile tilapia (Oreochromis niloticus) decreased T4 plasma level. It has been shown that monocrotophos (MCP), an organophosphate pesticide, decreased plasma TT3 levels and TT3-TT4 ratios in male goldfish (Carassius auratus) and had no effect on plasma TT4 levels (Zhang et al. 2013). It was also determined that exposure to malathion (10 and 20 ppm) and BHC (8 ppm) decreased plasma T4 level. It was also reported that fish exposed to BHC had a significant decrease in plasma T3 level (Yadav and Singh 1986). As with the results of the current study, other studies have also found that some pesticides reduce T3 and T4 activity levels in freshwater fish (Zhang et al. 2013; Khatun and Mahanta 2014; Ghelichpour et al. 2017; Nugegoda and Kibria 2017).
In this study and other studies, it has been reported that fish exposed to pesticides show a significant decrease in both TSH levels and T3 and T4 plasma levels compared to the control group. The increase and decrease in TSH can be explained by negative feedback arrangements (Wiersinga 2000). Because T4 decrease in plasma and/or lower TH production level by the pituitary, TSH increase can be expected (Patiño et al. 2003; Teles et al. 2005; Oliveira et al. 2011). Simultaneously, the decrease in plasma T3 level may have occurred due to the decrease in T4 synthesis or secretion (Li et al. 2008). Additionally, the decrease in plasma TT3 and TT4 levels because of increased exposure to NaPT may be due to possible changes in peripheral TH deiodination or metabolism because of the negative feedback mechanism. It has been shown that toxicological stress can affect the activity of 5'-deionidase (deio), which converts T4 to T3, by changing gene expression in fish (Wiersinga 2000; Wei et al. 2008; He et al. 2012). In the evaluations of the studies, it is stated that the decrease in the synthesis of TT3 and TT4, pesticides and pollution induces hyperplasia and hypertrophy of the follicular epithelium in the thyroid tissues, cause thyroid endocrine disruption, which causes an imbalance in T4 and T3 levels. Therefore, we hypothesise that NaPT may have had a cytotoxic effect on thyroid gland follicles. Simultaneously, anti-thyroid peroxidase antibodies against TSH receptors may be synthesised. Moreover, stimulated enzymatic metabolism of T3 in the liver may have reduced circulating TT3 levels (Zhang et al. 2014).