Toxicity Indicators

Ceriodaphnia, commonly known as water fleas, is used as a test organism for studying toxicity in freshwater aquatic systems. The U.S. EPA recommends using Ceriodaphnia in all three phases of acute TIEs (Zuiderveen, 1994). 

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REDUCED Acute toxicity Indications for use Chemical identity 10 kg... 

LD5f (median lethal dose) A standard measure of toxicity indicating the dose of a substance that will kill 50% of a group of test organisms. 

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). 

The committee concluded that the best evaluation for this purpose was a 90-day study in rats. An ADI of 0 to 2 mg/kg body weight was allocated based on a NOEL of 200 mg/kg body weight per day (the highest dose tested in the study) and a safety factor of 100. Although the ADI was based on the results of a shortterm study, the supporting data and lack of effects at much higher doses in some studies (e.g., a study of developmental toxicity) indicated that the safety factor of 100 was appropriate. 

Transformation Rates. A literature search was conducted to determine rates of oxidation, hydrolysis, photolysis, and biodegradation. When no values were found, we made estimates based on our experience, known rates for similar compounds, and structure-activity relationships. In cases where there was great uncertainty, a transformation rate of zero was assumed so that the compound would be considered persistent. This would force a more detailed fate assessment to be conducted if considerations of toxicity indicated that the compound might be hazardous. 

Several studies conducted in children known to have lead toxicity, indicate that nephropathy occurs in children only at PbB >80 pg/dL, and usually exceeding 120 pg/dL (NAS 1972). 

For offsite equipment the scores 0-3 have been used instead of scores 0-4 for ISBL equipment (HeikkilS and Hurme, 1998b), since the offsites represent only one third of all losses (Instone, 1989) and are therefore not as essential as ISBL. Also much of the risks of OSBL are due to the large inventory of flammable or toxic chemicals, which are discussed by the inventory, flammability and toxicity indices, not by the Equipment Safety Index. Also the equipment of same size is probably safer in OSBL than in ISBL because of the larger spacings in layout. 

Toxicity indicators, 23 112-114 Toxicity inhalation tests, 10 660 Toxicity studies acute, 25 217 chronic, 25 218 short-term repeated, 25 217 subchronic, 25 217-218 Toxicity units (TU), 25 887 Toxic materials, 21 833-836... 

In summary, the different joint effect models of multicomponent pollutant mixtures (i.e., the toxic unit, additive and mixture toxicity indices) were presented. Using such models to analyze the joint effect of a group of toxic and carcinogenic organic compounds such as polycyclic aromatic hydrocarbons will be presented and evaluated in Sect. 3.2. 

Maintenance dose 0.125-0.25 mg PO/IV qd low potassium or magnesium levels potentiate toxicity reduce dose in renal failure toxicity indicated by nausea, headache, visual disturbances (yellow-green halos), ventricular arrhythmias. Quinidine, verapamil, and amiodarone elevate digoxin level. 

The LDso for rats was 5.4ml/kg the low oral toxicity indicates that there is practically no likelihood that toxic amounts of these materials would be swallowed in ordinary handling and use. ... 

Much of the data related to the mechanism of hexachlorobutadiene toxicity indicate that the intermediates produced by modification of the S-1,1,2,3,4-pentachlorodienyl cysteine derivative are responsible for the observed effects on the proximal tubules of the nephrons. The cysteine derivative is formed from the hexachlorobutadiene conjugate in the liver, intestines, and/or kidney through the action of yglutamyl transferase which removes the glutamate from the glutathione tripeptide followed by the action of a peptidase that removes the glycine from the carboxy terminus. 

The test in which selective concentrations were used as a measure of toxicity indicated that most of the toxic hydrocarbons could be made selective by diluting them in a nontoxic oil. It was foimd in further tests with the aromatics diethylbenzene, tetrahydro-naphthalene, and dimethylnaphthalene that the greenhouse results could be duplicated on field-grown carrots and weeds. 

Figure 2.8 Dose-response curves for pharmacological effect and toxic effect, illustrating the EDS0 and TD50. The proximity of the curves for efficacy and toxicity indicates the margin of safety for the compound and the likelihood of toxicity occurring in certain individuals after doses necessary for the desired effect.

Human exposures resulting in toxicity indicate that the main target organs are liver and kidney (lARC, 1986). Sublethal exposure also causes central nervous system depression (Imberti et al., 1987 Lucantoni et al., 1992). In a case series of 10 painters or engineers with contact allergic dermatitis, all patients demonstrated a positive response to... 

As a rule, the highest concentrations of a poison are found at the site of administration. A large quantity of drug in the GI tract and liver indicates oral ingestion. The gastrointestinal (GI) tract may contain large amounts of unabsorbed toxicant. Cases that involve the oral administration of toxicants indicate analysis of GI contents. However, the presence of toxic material in the GI tract does not provide sufficient evidence that the agent is the cause of death. Absorption and transport of the toxicant to the site of action must be demonstrated. Blood and tissue analysis is necessary and would still be paramount. 

Benthic taxa exhibiting significant differences in abundance (at a = 0.05) between reference and exposure areas were noted. If a taxon was considered to be relatively more tolerant of pollution (such as enrichment in pulp mill effluent), it was listed as an Enrichment Indicator Organism . On a scale from 1 to 10, these taxa have pollution tolerances from 6 to 10 (Moody, 2000). If a taxon was considered to be relatively less tolerant of pollution, it was listed as a Toxicity Indicator Organism . These taxa have pollution tolerances from 1 to 5. Species representing both types of indicator groups were found to show potential effluent-related effects at the Kimberly-Clark mill. The total number of potential effluent-related effects is calculated for comparison with the LTF method case study in Section 7.2. 

Toxicity indicator organism Ref > Exp Monoporeia Stylodrilus heringianus Yes (Ref> Exp)1... 

The results of toxicity assays enable the ecotoxicological quality of environmental samples to be assessed on the basis of the value (expressed as a percentage) of the observed effect of toxic activity, for example, bioluminescence inhibition, algal growth inhibition, and lethalities of crustaceans, as well as estimated toxicity indices such as L(E)C20, L(E)C50, or toxicity unit (TU). 

Various techniques, such as graphic illustrations (e.g., isobolograms), mixture toxicity indices (e.g., an additivity index), formulas, or fully parameterized models, exist for predicting an expected combined effect based on concentration addition or response addition (for review, see Bodeker et al. 1990). The quantitative relationship between the expected combined effect calculated according to concentration addition or response addition depends (in addition to other factors) primarily on the steepness of the concentration response relationship of the individual components (Drescher and Bodeker 1995). Concentration addition predicts a higher combined effect as compared to response addition when the mixture components have steep concentration response relationships, whereas the opposite is true for flat concentration response relationships of the mixture components. 

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