Toxicity immunotoxicity

Short- to medium-term exposures have shown neurotoxicity, developmental toxicity, immunotoxicity, and endocrine disruption to be relevant end-points, although the degree of each of these toxic end-points differs across the group as a whole. 

The predominant toxic end-points vary among the different organotins and include neurotoxicity, reproductive and developmental toxicity, immunotoxicity,... 

Short- to medium-term exposure has shown neurotoxicity, developmental toxicity, immunotoxicity, and endocrine disruption to be relevant end-points. Table 24 summarizes the critical studies for each compound and identifies NOAELs or LOAELs. The degree of each of the toxic end-points differs across the group as a whole. For example, tributyltin is well established as an aromatase inhibitor, and dibutyltin appears to have some potency also (exact characterization of the endocrine disrupting capacity of dibutyltin alone is difficult because of the presence of tributyltin as an impurity). Monobutyltin and mono- and dioctyltins have no aromatase inhibiting capacity in in vitro tests. No data are available for this end-point for the methyltins. 

Toxicology. Chlorinated dibenzo-p-dioxins (CDDs) cause chloracne, may cause hepato-toxicity, immunotoxicity, reproductive toxicity, developmental toxicity, and central nervous system toxicity, and are considered to be a human carcinogen. 

Safety of the product itself for the target organism, the user (who applies it) or the environment is addressed by a range of preclinical and clinical assessments which depend on the product and its use pattern. The range of safety features to be assessed includes local and systemic tolerance, acute and chronic toxicity, mutagenicity and tumorigenicity, reproductive toxicity, immunotoxicity and, for veterinary medicinal products, also the ecotoxicity. The safety tests will be described in more detail in a separate chapter below on preclinical pharmacological and safety test procedures. 

Indoor dust is a primary route of human exposure to BFRs (Lorber 2008 Harrad et al. 2010 Covaci et al. 2009) several studies have linked indoor dust concentrations of BFRs with human body burdens (Wu et al. 2007 Johnson et al. 2010, 2013 Stapleton et al. 2012 Roosens et al. 2009). BFRs are associated with a wide range of adverse health effects, including endocrine disruption, reproductive/ developmental toxicity, immunotoxicity, and neurotoxicity (Bimbaum and Staskal 2004 Shaw et al. 2010 Covaci et al. 2009). 

Dioxins are prominent members of the class of polychlorinated hydrocarbons that also includes diben-zofuran, biphenyls and others. Dioxins are highly toxic environmental contaminants. Like others small planar xenobiotics, some dioxins bind with high affinity to the arylhydrocarbon (Ah) receptor. Dioxins activate the receptor over a long time period, but are themselves poor substrates for the enzymes which are induced via the Ah-receptor. These properties of the dioxins and related xenobiotics may be important for the toxicity of these compounds. Dioxins like 2,3,7,8-tetrachloro-p-dibenzodioxin can cause persistent dermatosis, like chloracne and may have other neurotoxic, immunotoxic and carcinogenic effects. 

Organotin Neurotoxicity Developmental toxicity Endocrine disruption Immunotoxicity... 

Immunotoxicity. Only a single case report of skin allergy to methyl parathion has been reported in humans (Lisi et al. 1987). No studies are available in humans exposed to methyl parathion via the inhalation or oral route. Based on limited animal studies, immunotoxicity may be a sensitive end point of methyl parathion-induced toxicity (Shtenberg and Dzhunusova 1968 Street and Sharma 1975). Thus, humans may be at risk for adverse immunological effects following exposure to methyl parathion. The limited information available on the effects of combined exposure to methyl parathion suggest the its toxicity is not route-dependent. Therefore, there is no reason to suspect that the immunotoxic effects observed following oral exposure of animals are route-specific. 

These results demonstrate that immunotoxicity may be a sensitive end point of endosulfan-induced toxicity following exposure to low doses for sufficient durations. The highest NOAEL value and all reliable LOAEL values for immunological effects in each species in each duration category are recorded in Table 2-2 and plotted in Figure 2-2. 

Immunotoxicity. Limited information is available regarding the effects of endosulfan on the human immune system. However, specially designed studies using rats indicate that both humoral and cellular immune responses are depressed by ingested endosulfan at doses that do not induce any overt signs of toxicity (Banerjee and Hussain 1986,1987). In vitro studies support the possibility that endosulfan affects immune system function (Das et al. 1988). These results demonstrate that immunotoxicity may be a more sensitive end point of endosulfan-induced toxicity than other end points, and humans may be at risk for adverse immune effects following exposure to endosulfan. An intermediate-duration oral MRL was derived based on the observation of depressed immune responses (Banerjee and Hussain 1987). 

Vos JG, Krajnc El, Beekhof PK, et al. 1982. Methods for testing immune effects of toxic chemicals Evaluation of the immunotoxicity of various pesticides in the rat. In Miyamoto J, Kearney PC, eds. Pesticide chemistry Human welfare and the environment. Oxford, England Pergamon Press, 497-504. 

The toxicology of PCBs is complex and not fully understood. Coplanar PCBs interact with the Ah-receptor, with consequent induction of cytochrome P4501A1/2 and Ah-receptor-mediated toxicity. Induction of P4501A1 provides the basis of valuable biomarker assays, including bioassays such as CALUX. Certain PCBs, for example, 3,3, 4,4 -TCB, are converted to monohydroxymetabolites, which act as thyroxine antagonists. PCBs can also cause immunotoxicity (e.g., in seals). 

Toxic equivalency factors (TEFs) are estimated relative to 2,3,7,8-TCDD, which is assigned a value of 1. They are measures of the toxicity of individual compounds relative to that of 2,3,7,8-TCDD. A variety of toxic indices, measured in vivo or in vitro, have been used to estimate TEFs, including reproductive effects (e.g., embryo toxicity in birds), immunotoxicity, and effects on organ weights. The degree of induction of P450 lAl is another measure from which estimations of TEF values have been made. The usual approach is to compare a dose-response curve for a test compound with that of the reference compound, 2,3,7,8-TCDD, and thereby establish the concentrations (or doses) that are required to elicit a standard response. The ratio of concentration of 2,3,7,8-TCDD to concentration of test chemical when both compounds produce the same degree of response is the TEF. Once determined, a TEF can be used to convert a concentration of a dioxin-like chemical found in an environmental sample to a toxic equivalent (TEQ). 

Mineral Oil Hydraulic Fluids. There is limited information on the toxicity of mineral oil hydraulic fluids in humans. A single case report of a child accidentally ingesting a single dose of automotive transmission fluid provides limited information on death and systemic effects. A case-control study provides some information on the carcinogenicity of mineral oil hydraulic fluids. The study population was exposed via inhalation and dermal routes. An occupational exposure study provides information on neurotoxicity following chronic dermal exposure. Information on the toxicity of mineral oil hydraulic fluids is limited to a series of inhalation, oral, and dermal acute-duration exposures. These studies provide information on death, systemic effects, and neurotoxicity by inhalation, oral, and dermal routes, and immunotoxicity following dermal exposure. 

Several studies have suggested that some critical adverse effects like peroxisome proliferation, hepatotoxicity, immunotoxicity, and developmental toxicity may be associated with chemical exposure to PFCs, particularly to PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoic acid), two ubiquitous persistent organic pollutants with possible environmental and human health risks. 

In summary, OTC toxicity either toward animal organs or as drugs appears in four broad target areas, namely neurotoxicity, hepatoxicity, immunotoxicity and cutaneous toxicity10. Although other effects occur in select species or at high dose levels, their importance is minor compared to the four areas listed above. 

Phenyltin compounds significantly inhibit natural killer cell function and possible natural killer cell-mediated immunotoxic potential of these compounds in humans (Whalen et al. 1999). The toxic potential followed the order of triphenyltin > diphenyltin > monophenyltin however, phe-nyltins were less toxic than butyltins to human natural killer cells (Whalen et al. 1999). 

Data for PCP and terrestrial wildlife are incomplete and — in view of the large interspecies variations in sensitivity — need to be collected. Research is needed on reproductive effects in animals following inhalation exposure to PCP additional acute and intermediate toxicity testing chronic duration exposure studies on cancer induction, genotoxicity, and immunotoxicity and the development of alternate biomarkers of PCP exposure and antidotes (WHO 1987 USPHS 1994). Until the results of these studies become available, it seems reasonable to apply to wildlife the same levels recommended for human health protection. 

In all tested organisms, PCBs — especially PCBs with 2,3,7,8-TCDD-like activity — adversely affected patterns of survival, reproduction, growth, metabolism, and accumulation. Common manifestations of PCB exposure in animals include hepatotoxicity (hepatomegaly, necrosis), immunotox-icity (atrophy of lymphoid tissues, suppressed antibody responses), neurotoxicity (impaired behavior and development, catecholamine alterations), increased abortion, low birth weight, embryolethality, teratogenicity, gastrointestinal ulceration and necrosis, bronchitis, dermal toxicity (chloracne, edema,... 

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