**3.5 Pyrethorids**

250 Pesticides in the Modern World - Risks and Benefits

pathogenic bacteria resulted in a higher disease resistance than those injected with the bacteria

Chlorinated dioxins, as typified by the most potent isomer TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin), are also very toxic for fish. Injection of 0.1-10 µg TCDD/kg bw to rainbow trout resulted in very little changes in humoral and cellular immune responses (Spitsbergen et al., 1986). However, while the C-reactive protein levels in serum were increased the leucocyte production of IFN was unchanged (Winkelhake et al., 1983). In common carp, TCDD injection produced histological alterations including increase of melano-macrophage centres and reduction of lymphocyte numbers (van der Weiden et al., 1994). Further studies have also evaluated fish tissue alterations and CYP1A staining patterns have been described in European flounder (*Platichthys flesus*) and gilthead

Some studies have also evaluated the immunotoxicological effect of other OCs. In the case of furans (PCDF), most authors have focused on other fish toxicity tests rather than in immunotoxicology. Endosulfan exposure produces developmental and neurological disorders and acts as endocrine disruptor. Rainbow trout leucocyte treatment with endosulfan inhibited the lymphoproliferative activity where the B-cells were more sensitive than the T lymphocytes (O'Halloran et al., 1996). In another study, crimson-spotted rainbowfish (*Melanotaenia fluviatilis*), golden perch (*Macquaria ambigua*) and Murray cod (*Maccullochella peelii*), but not silver perch (*Bidyanus bidyanus*), leucocytes showed decreased phagocytosis after endosulfan treatment (10 mg/L) (Harford et al., 2005). *In vivo* treatment of Nile tilapia for 96 h at 7 ppb produced an increased phagocytosis and ROS production by spleen leucocytes, IgM levels and production of IL-2-like, but at the same time reduced the

OPs are insecticides used world-wide as an alternative to the persistent and more bioaccumulative OCs. They are potent neurotoxic and immunotoxic since are irreversible acetylcholinesterase inhibitors (Galloway and Handy, 2003). Malathion exposure (0.2-0.8 mg/L) of medaka resulted in reduced number of antibody-forming cells but unchanged circulating leucocyte numbers and T-cell proliferation (Beaman et al., 1999). Vaccinated Nile tilapia exposed to malathion or diazinon presented lower blood cell counts, phagocytosis and antibody levels than those unexposed (Khalaf-Allah, 1999). Diazinon exposure of bluegill had biphasic effects with immune response increases at low concentrations and depressions at high dosages (Dutta et al., 1997). In Nile tilapia, Girón-Pérez et al., (2007, 2008, 2009) have showed that diazinon altered the spleen counts and lymphocyte proliferation, serum IgM and lysozyme levels, phagocytic activity and respiratory burst depending on the exposure dose and time. Chlorpyrifos displayed little immunotoxicity, although there was a dose-dependent reduction in Murray cod lymphocytes (Harford et al., 2005). Nile tilapia exposed to the LC50 failed to change blood parameters but the phagocytic activity was significantly reduced (Girón-Pérez et al., 2006). Chlorpyrifos exposure produced an up-regulation of hsp60, hsp70 and hsp90 genes, related to the cellular stress response in Chinook salmon. Moreover, the cytokine (IL-1b, TGF-beta, Mx and insulin growth factor (IGF)-I) gene expression was unaltered or down-regulated but not affected the virus susceptibility of the fish (Eder et al., 2008, 2009). Dichlorvos and trichlorfon insecticides have been used in aquaculture against ectoparasites in the past. Trichlorfon exposure decreased the serum lysozyme, lymphocyte proliferation, respiratory burst and

suggesting a direct effect on the immune response (Ekman et al., 2004).

seabream (Grinwis et al., 2000; Ortiz-Delgado & Sarasquete, 2004).

spleen viability and relative weight (Tellez-Bañuelos et al., 2009, 2010).

**3.4 Organophosphorous pesticides (OPs)** 

Pyrethroids are extensively used insecticides since they are very stable and produce low mammalian toxicity but this is very high for aquatic animals (Bradbury & Coats, 1989). Among them, deltamethrin injection to *Ancistrus multispinis* increased peritoneal leucocyte numbers and production of RNI by macrophages (Pimpão et al., 2008). Short exposure to deltamethrin (30 min., 1-4 µg/L) of rainbow trout resulted in decreased serum lysozyme and IgM levels (Siwicki et al., 2010). Water exposure of rohu (*Labeo rohita*) to alphapermethrin produced a reduction in lysozyme activity and resistance to bacteria (Nayak et al., 2004). Rainbow trout exposure to cypermethrin failed to alter any of the immune parameters (Shelley et al., 2009). Esfenvalerate exposure produced an up-regulation of hsp60, hsp70 and hsp90 stress genes, down- or non-regulated cytokines and unaffected the virus susceptibility of the Chinook salmon (Eder et al., 2008, 2009). Using microarrays, delta smelt (*Hypomesus transpacificus*) exposure to esfenvalerate produced alterations in the expression of genes associated with immune responses, along with apoptosis, redox, osmotic stress, detoxification, growth and development (Connon et al., 2009).

#### **3.6 Organotins**

Organotin compounds or stannanes are chemical compounds based on tin (Sn) with hydrocarbon substituents showing different toxic effects. TBT (triorganotins) is specially important since it has been widely used as marine anti-biofouling agent. Injection of 0.01-1 mg TBT (tributyltin)/kg bw of channel catfish altered leucocyte counts, NCC, phagocytic and respiratory burst activities, production of specifc antibodies and number of antibodyproduceing cells (Rice et al., 1995). TBT treatment signinficantly reduced the lymphocyte numbers in spleen, the thymus volume and the leucocyte NCC activity in European flounder (*P. flesus*) (Grinwis et al., 2000). In rainbow trout, *in vitro* incubation with 2.5-500 ppb TBT and DBT (dibutyltin) reduced the lymphoproliferation activity in pronephros and spleen but failed to affect the NCC activity showing DBT higher toxicity than TBT (O'Halloran et al., 1998). *In vitro* incubation of several Australian fish head-kidney leucocytes with TBT or DBT depressed the phagocytic activity and reduced the numbers of lymphocytes and granulocytes (Harford et al., 2005).

#### **3.7 Other chemicals**

Herbicides are still widely used and end in aquatic environments producing many physiological alterations but little studies have focused on their immunotoxicological effects in fish. Herbicides mixture, containing atrazine, simazine, diuron and isoproturon, exposition of goldfish increased spleen and head-kidney ROS production and serum lysozyme but reduced the specific antibodies and resistance to bacterial infections (Fatima et al., 2007). Atrazine exposure of silver catfish resulted in decreased phagocytosis and

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resistance to disease (Kreutz et al., 2010) whilst failed to do so in common carp (Cossarini-Dunier et al., 1987; Cossarini-Dunier & Hattenberger, 1988). Phenols are another group of toxics. Phenol, pyrocatechol and hydroquinone decreased the cell-mediated cytotoxic activity of spleen lymphocytes in common carp (Taysse et al., 1995), pentachlorophenol reduced macrophage production of cytokines in goldfish (Chen et al., 2005) but activated phagocytosis and unaltered other immune functions and disease resistance in rainbow trout (Shelley et al., 2009). Endocrine disrupting chemicals produce population decline, an increasing incidence of cancer, inhibition of reproductive function, and developing disruption of the immune and nervous systems. However, there are very limited data concerning the role of endocrine disrupting chemicals on aquatic organism, including the fish immune response. Zebrafish embryos exposed for 3 days to 17α-ethynyestradiol, permethrin, atrazine and nonylphenol (0.1-12.5 μg/L) altered the expression of immunerelevant genes (TNFα, IFN, IL-1β, IL-8, CXCL-Clc, CC-chemokines, iNOS, etc.) indicating their single and combined effects upon fish immune response (Jin et al., 2010).
