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Emerging methodologies for assessment of complex mixtures: application of bioassays in the Integrated Air Cancer Project.

The assessment of complex mixtures of environmental pollutants requires new interdisciplinary strategies. Integration of bioassay methodologies into these strategies is an important tool that provides direct evidence of the toxicity of a mixture. Short-term genetic bioassays are now widely used in the cancer assessment of complex mixtures. New and emerging interdisciplinary methodologies for assessing complex mixtures using bioassays are illustrated by the U.S. EPA's Integrated Air Cancer Project (IACP). The goals of this project are to identify the major airborne carcinogens and their emission sources and to improve the methodology and data available for human exposure and risk assessment from airborne carcinogens. The research effort is focused primarily on characterizing the impact of complex mixtures of products of incomplete combustion, including gaseous, semi-volatile, and particle-bound organic species. Short-term genetic bioassays have been integrated into several analysis strategies, including environmental biomonitoring; bioassay-directed fractionation/characterization; transformation studies; source apportionment; and exposure, dosimetry, and risk assessment.

Air Pollutants↗

Mixtures of nickel and cobalt chlorides induce synergistic cytotoxic effects: implications for inhalation exposure modeling.

Workers are often simultaneously exposed to two or more chemicals, yet little is known about the toxicity of most chemical mixtures. The traditional assumption, in the absence of further information, has been that the chemical components of a mixture have mutually independent effects, and the toxic response to multiple chemicals is additive. The data presented here show that mixtures of NiCl(2) and CoCl(2) induce a synergistic (that is, greater than additive) toxic response in cell culture. Immortalized alveolar epithelial type II cells were incubated for 4 h with various concentrations of either NiCl(2), CoCl(2), or NiCl(2) and CoCl(2) together, and cell viability assessed 24 h later. The LD(50) for NiCl(2) was 5.7 mM. CoCl(2), with an LD(50) of 1.1 mM, was about five times more potent than NiCl(2). Mixtures of NiCl(2) and CoCl(2) decreased cell viability synergistically. For example, a mixture of 750 microM NiCl(2) and 750 microM CoCl(2) reduced cell viability by more than three times the value predicted by the additive approach. We used concentration-response data from these studies in a mathematical model; this model describes the equivalent inhalation exposure to an aerosol composed of a mixture of chemicals with different toxicities and also accounts for synergistic responses to these chemicals. Our results along with previous studies using an animal model suggest that these synergisms should be taken into account when conducting future exposure assessments.

Air Pollutants↗

In vivo studies on halogen compound interactions. III. Effect of carbon tetrachloride plus 1,2-dichloroethane on liver necrosis and fatty accumulation.

The effect of a single dose of carbon tetrachloride (CT), 1,2-dichloroethane (DCE) and the mixture on liver toxicity was investigated. The co-presence of both toxins exerts a more than additive effect on liver necrosis and on TBA-reactive substances produced by liver homogenates incubated at 37 degrees C. Both these effects are prevented in animals treated with vitamin E. The liver GSH is not involved in the synergistic action. The liver triglyceride levels of rats treated with the mixture are lower than in those treated with CT alone. This finding cannot be explained either by an improvement in the lipoprotein secretion or by the fact that the liver receives less NEFA. It is thus likely that the apparent protection against liver steatosis is the sign of more severe damage to the liver cell that partially blocks triglyceride synthesis. The mixture composed of CT+DCE exerts a potentiating action on liver toxicity with CT+DCE having the same characteristics as those, as previously reported, exerted by the co-presence of CT+DBE.

Alanine Transaminase↗

[Impacts and impact mechanisms of "dioxins" in humans and animals].

"Dioxins" are used to specify polychlorinated dibenzo-p-dioxins (PCDD), dibenzo-furanes (F) and dioxin-like polychlorinated biphenyls (PCB's). Many of the congeners proved to be highly toxic; 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) is the most toxic congener, and probably the most toxic compound ever synthesized by man (the natural occurance of this substance is very low). The total concentration/-toxicity of a mixture of congeners (WHO-PCDD/F-TEQ, or including the PCB's WHO-PCDD/F-PCB-PCB-TEQ) is calculated by addition of the individual concentrations multiplied by respective toxicity equivalence factors TEF; the most toxic congener TCDD is defined as 1. The tolerable weekly intake TWI set by the European Commission is 14pg WHO-PCDD/F-TEQ/kg bw. The "body burden" of adults in industrial countries is about 2-6 ng WHO-PCDD/F-TEQ/kg bw., or about double this value if PCB's are also considered. There is a very broad range of toxic effects of "dioxins". Many of the congeners can induce toxic responses at very low "body burdens". The most sensitive effects are immunosuppression, developmental and reproductive toxicity, as well as neurological behavioral effects. These effects occur at "body burdens" whih are close to background exposure of the human. Cancerogenic effects are induced at higher exposure (Seveso, industrial exposure). TCDD was considered a "complete carcinogen" by the IARC (Group 1). There is a broad range of carcinogenic effects, and there is no "hallmark" effect. Most toxic effects induced by TCDD are mediated by binding to the Ah-receptor (Ah-R) which binds together with a second protein, ARNT, to the respone elements of a number of target genes, and thus modulates gene expression. "Dioxins" are strong promotors, but weak initiators. The multitude of interactions of the Ah-R and ARNT ("receptor cross-talk") results in numerous molecular and cellular effects. The TCDD-Ah-R complex can also bind to the response element of the estrogen receptor, and thus can block the effects of es-trogens. This explains the fact that TCDD can be an estrogen antagonist reducing or preventing mamma carcinoma. Other Ah-R ligands occur in vegetables (e.g. indoles, flavones) and will possibly be developed in the future as functional substances. PCB's have similar properties to TCDD if they can exist in a planar configuration (dioxin-like PCB's). The non-dioxin-like PCB's always occur together with "dioxins"; their toxixty cannot be adequately determined although they occur in high concenrations. The consumption of food contaminated with "dioxins" need not directly lead to a toxic effect. Due to the continous cumulation of "dioxins" repeated ingestion of contaminated food could result in an increase of the "body burden" and thus chronic toxicity. This shows that the exposure of the human to dioxins should be minimized wherever possible.

Animals↗

Synthesis and degradation of aflatoxins by Aspergillus parasiticus. II. Comparative toxicity and mutagenicity of aflatoxin B1 and its autolytic breakdown products.

A crude mycelial protein extract from a 16-day-old culture of A. parasiticus, on purification, lost 50% of its ability to degrade aflatoxin B1. The addition of hydrogen peroxide increased this activity to 97% of that of the crude extract. Ducklings dosed orally with aflatoxin extracts from 14- and 20-day-old cultures containing 46 micrograms or more of aflatoxin B1 developed enlarged livers, haemorrhaged and died in less than 10 days, giving and LD50 of 17.5 and 17.1 micrograms aflatoxin B1 per 50 g body weight respectively for each extract. When pure aflatoxin B1 was mixed with either the crude or purified mycelial protein extract the aflatoxin B1 level was decreased by 29% as was the toxicity of the mixture. The main breakdown product of aflatoxin B1 was isolated and was shown to have an RF value of 0.34, was non-fluorescent, and was non-toxic for ducklings at oral doses as high as 400 micrograms per 50 g body weight. The mutagenic effect of aflatoxin B1 on Salmonella typhimurium was relative to its concentration. The main breakdown product of aflatoxin B1 was non-mutagenic.

Aflatoxin B1↗

Evaluation of lethality and genotoxicity in the freshwater mussel Utterbackia imbecillis (Bivalvia: Unionidae) exposed singly and in combination to chemicals used in lawn care.

Many chemicals, including fertilizers, herbicides, and insecticides, are routinely applied to turf in the care and maintenance of lawns. These chemicals have the potential to leach into nearby surface waters and adversely affect aquatic biota. In this study, we evaluated the lethal and genotoxic effects of chemicals used in lawn care on an early life stage of freshwater mussels (Utterbackia imbecillis). The chemicals tested were copper and commercial formulations of atrazine, glyphosate, carbaryl, and diazinon. Mussel glochidia were exposed to chemicals singly or in combination (equitoxic and environmentally realistic mixtures) for 24 h and toxic interactions were evaluated with Marking's additive index. Genotoxicity was quantified with the alkaline single-cell gel electrophoresis assay (Comet assay). In acute tests, copper was the most toxic of all chemicals evaluated (LC50 = 37.4 microg/L) and carbaryl was the most toxic of all pesticides evaluated (LC50 = 7.9 mg/L). In comparison to other aquatic organisms commonly used in toxicity tests (e.g., amphipods, cladocerans, and chironomids), mussel glochidia were as or more sensitive to the chemicals evaluated with the exception of diazinon, where mussels were observed to be less sensitive. The combined toxicity of equitoxic and environmentally realistic mixtures to mussels was additive. Genotoxic responses were observed in mussels exposed to copper, atrazine and diazinon at levels below their respective no-observed-effect concentrations. Together, these data indicate that freshwater mussels are among the most sensitive aquatic organisms tested for some chemicals commonly used in lawn care and that DNA damage may be useful as a screening tool to evaluate potential sublethal effects of lawn care products on non-target aquatic organisms.

Animals↗

Effect of major ions on the toxicity of copper to Hyalella azteca and implications for the biotic ligand model.

The effect of major ions (Ca, Mg, Na, and K) and pH on Cu toxicity (LC50) to Hyalella azteca was determined in 1 week exposures. The simplest equation for describing Cu toxicity is a linear relationship between the total dissolved Cu LC50 and Ca and Na in water, ignoring pH. This equation would be useful in tier one of a two-tiered approach; if the measured dissolved Cu exceeds the value predicted from the equation, the sample should either be tested for toxicity, or a more detailed chemical speciation analysis can be conducted. The data were not consistent with a single-binding-site biotic ligand model, assuming that toxicity was due to the free Cu ion alone. However, toxicity could be predicted using a two-binding-site model. This requires separate coefficients to account for the effects of Ca and Na at low and high pH values (6.5-8.4), corresponding to the different binding sites (Mg and K did not affect toxicity). The single-binding-site BLM does not allow for this. Toxicity of Cu hydroxide or carbonate complexes does not need to be invoked, but cannot be excluded, and several models invoking the toxicity of these complexes can also explain the data. The free ion LC50 is strongly dependent on pH, but the LC50 for total dissolved Cu is almost pH independent. The effects of Ca and Na on the free ion LC50 are very different at high and low pH (contrary to single-site biotic ligand model predictions), but similar for total dissolved Cu. Published data suggest that the same model, with different coefficients, can also be applied to Daphnia and fish. A more critical evaluation of the effects of cations at both low and high pH for organisms other than Hyalella is needed to determine if the BLM needs to be adjusted to incorporate more than one binding site for other species as well. Hydrogen ions reduce the toxicity of free Cu ions to Hyalella, but Cu also reduces the toxicity of hydrogen ions. A mixture model accounting for the joint toxicity of Cu and pH, as well as their mutual antagonistic effects, is presented.

Amphipoda↗

[Effect of mycotoxin T-2 on bioluminescence intensity of bacteria].

The acute and chronic toxicity of T-2 was studied by bioluminescent method with the use of two strains of luminous bacteria--P. phosphorum Sq3 u V. fischeri F1 as biological objects. It was shown that in acute experiments after 10 min incubation of bacteria in the presence of T-2 the bioluminescence inhibition on the 50% level was observed at the toxin concentration equal to 12 mg/mL. In chronic experiments such a level of bioluminescence inhibition was registered after 16 hours incubation at the toxin concentration of 18 mg/mL. T-2 toxicity was also investigated in the presence of different serum albumin concentrations. It decreases with the increase of albumin concentration at the short term of incubation (5 min) of the mixture to be analyzed. In case of the longer term of incubation (up to 30 min) of this mixture T-2 toxicity was restored. Probably, it is a result of destruction of protein-toxin complex, which is, evidently, reversible and may be characterized by some index. It is necessary to emphasize that the sensitivity of T-2 analysis increases under the decrease of pH value up to lower bacterial physiological level, i.e. to 5-5.5. The revealed abilities of T-2 toxin effect on the intensity of bacterial bioluminescence may be used under the development of instrumental analytical approach on the basis of biosensor technology for testing this toxin in the environment. Taking into account the analysis simplicity and rapidity, such analytical device may have a perspective for wide practical application.

Environmental Monitoring↗

Performance evaluation of the Scent Transfer Unit (STU-100) for organic compound collection and release.

The Scent Transfer Unit (STU-100) is a portable vacuum that uses airflow through a sterile gauze pad to capture a volatiles profile over evidentiary items for subsequent canine presentation to assist law enforcement personnel. This device was evaluated to determine its ability to trap and release organic compounds at ambient temperature under controlled laboratory conditions. Gas chromatography-mass spectrometry (GC-MS) analyses using a five-component volatiles mixture in methanol injected directly into a capture pad indicated that compound release could be detected initially and 3 days after the time of collection. Additionally, 15 compounds of a 39-component toxic organic gaseous mixture (10-1000 parts per billion by volume [p.p.b.(v)]) were trapped, released, and detected in the headspace of a volatiles capture pad after being exposed to this mixture using the STU-100 with analysis via GC-MS. Component release efficiencies at ambient temperature varied with the analyte; however, typical values of c. 10% were obtained. Desorption at elevated temperatures of reported human odor/scent chemicals and colognes trapped by the STU-100 pads was measured and indicated that the STU-100 has a significant trapping efficiency at ambient temperature. Multivariate statistical analysis of subsequent mass spectral patterns was also performed.

Animals↗

Prediction and experimental validation of acute toxicity of beta-blockers in Ceriodaphnia dubia.

Acute toxicity of beta-adrenoceptor blockers (beta-blockers) was studied with beta-blockers as single compounds or in mixture using the standardized acute 2-d Ceriodaphnia dubia immobility test. The tested compounds were selected according to their selectivity for the beta1-adrenoceptor, with three beta1-selective blockers (acebutolol, atenolol, and metoprolol) and three non-beta1-selective blockers (nadolol, oxprenolol, and propranolol). The acute toxicity (median effective concentration) of the six single compounds ranged from 1.4 mg/L for propranolol to 163 mg/L for nadolol. According to European Union directive 93/67EEC, these values range from toxic for aquatic organisms to nonclassified. The more toxic compounds, propranolol and oxprenolol, are both characterized by a membrane-stabilizing activity, a strong affinity for the beta1-adrenoceptor, and a high octanol-water partition coefficient (log Kow). The property of beta-receptor selectivity seems not to be involved in the observed acute toxicity of the single compounds for C. dubia. Nevertheless, the toxicity of the selected compounds in mixture can be defined according to the beta1-selectivity. Two main joint effects have been detected: An independent action for the beta1-selective blockers, and an additive effect when either the nonselective beta1-selective blockers or the six compounds are tested together. The concentration addition model seems to be appropriate, providing a reasonable worst-case estimation of beta-blocker mixture toxicity for regulatory purposes.

Adrenergic beta-Antagonists↗

Occupational exposure limits in the context of solvent mixtures, consumption of ethanol, and target tissue dose.

Individuals are exposed to mixtures, and never to single chemicals. Depending on the composition of the elements of mixtures, significant toxicological interactions between the components may occur. These interactions are complex and often difficult to predict, ranging from synergistic to additive and subadditive interactions. The nature of the interactions needs to be evaluated as the target tissue dose of the active form of each chemical. PBPK modeling is an effective tool for determining the target tissue dose and evaluating these interactions when data are available for model development. Some of the interactions are pharmacokinetic in nature, affecting the disposition of other chemicals in the body. Other interactions can be pharmacodynamic in nature, altering the effects that other chemicals have on the organism. For many organic solvents, these interactions occur principally at the level of the metabolizing enzyme, cytochrome P-450 2E1 (CYP2E1). Many solvents are known to induce or inhibit CYP2E1, or both. Mixtures may be comprised of concomitant exposures to chemicals or from components encountered separately on-the-job, off-the-job, through the diet, and otherwise. Examples of mixtures where the exposure to separate components occurs off the job will be discussed, with special emphasis on ethanol consumption as a modifier of solvent pharmacokinetics. The present practice of the linear extrapolation of the toxicity of individual mixture components in the interpretation of occupational exposure limits will also be critiqued.

Alcohol Drinking↗

Effect of pesticide mixtures on in vitro nervous cells: comparison with single pesticides.

The toxicity of dimethoate, azinphos-methyl, diazinon, pirimiphos methyl, organophosphorus insecticides, and benomyl (a benzimidazole fungicide) singly and in mixture was studied in a human neuroblastoma cell line, SH-SY5Y. The cells were incubated for 30 min and 4 h with pesticides at concentrations ranging from 0.4 to 100 micrograms/ml, or with the same compounds mixed as follows: (a) dimethoate-diazinon-azinphos; (b) benomyl-pirimiphos; (c) all together. Pesticides in the mixtures were at the same concentration used when tested singly. Diazinon, azinphos-methyl and pirimiphos, but not dimethoate and benomyl, inhibited acetylcholine esterase (AchE) activity, whereas all the compounds inhibited protein synthesis in the following order: benomyl > azinphos > diazinon >> pirimiphos = dimethoate. The mixtures showed a toxicity on AchE activity at a maximum equal to that of the most active compound in the mixture. On the contrary, the mixture were more toxic than the single compounds on protein synthesis, and in certain cases potentiation occurred. Therefore, we can conclude that it is not feasible to predict the toxicity of pesticide mixtures on the basis of the results of the toxicity of single components.

Acetylcholinesterase↗

Risk assessment of chemical mixtures from a public health perspective.

Health risk assessment is the practice of evaluating the degree of danger associated with chemical exposure, whether the exposure is intentional (pharmacologic agents, pesticides) or unintentional (industrial/automobile by-products). Chemical exposure can either be to a single chemical or to complex mixtures such as industrial effluents, municipal wastes, jet fuels, gasoline, or mixtures of drinking water contaminants. The mixtures can be simple or complex; partially or completely characterized; and stable or varying in composition. Three different approaches are often used in health risk assessment of chemical mixtures (51 FR 33992-34054). These 3 approaches consist of (a) use of data on the specific mixture of concern; (b) use of data on a similar mixture; and (c) use of data on each component of the mixture. The individual component-based approach is by far the most often used because it allows the individual risks from each component to be combined, usually by dose or response additivity, to calculate an overall risk for the mixture. In addition, several innovative methods, such as the toxicity equivalency factor, relative potency, and even the use of indicator chemicals, are also employed. More recently, a binary weight-of-evidence approach has been proposed to evaluate potential interactions between the various components and to integrate them into the overall toxicity assessment of the mixture. Because no single approach is suitable for assessing the health risk associated with all the exposure scenarios associated with the various types of mixtures, the use of professional judgment is still imperative in conducting health risk assessments.

Drug Interactions↗

Psychiatric and neurological symptoms in workers occupationally exposed to organic solvents--results of a differential epidemiological study.

It is accepted knowledge today that repeated intoxication with organic solvents damages the central nervous system and causes persistent psycho-organic symptoms. That long-term but low-level occupational exposure--typical o painters and other blue-collar workers--can also induce such disorders has not generally been recognized. The present epidemiological study was undertaken to evaluate the possible neuropsychiatric effects of such exposure. 80 laquerers exposed to a mixture of industrial solvents (average hygienic effect 0.3) and 37 printers exposed almost only to toluene (average hygienic effect 1.0) were compared with a control group of 80 age-matched non-exposed subjects. In psychiatric interviews, the painters showed more mental symptoms. Fatigue, nervousness and lack of manual dexterity were most important and formed a typical neurasthenic syndrome. A general decrease in conduction velocity and action potential amplitude was also observed for the peripheral nerves. The printers showed a large decrease of the nerve action potential amplitude only for the sural nerve. No EEG abnormalities were found. Nor could any increase in mental symptoms be detected through psychiatric interviews compared to the controls. The results are interpreted as evidence for a CNS affection with consequent neuropsychiatric signs and symptoms after long-term occupational exposure to mixtures of industrial solvents below the current threshold limit values (TLV) but not after exposure to a single substance like toluene at about the TLV. The differential effects may be explained by synergistic amplification of the toxicity of solvent mixtures.

Adult↗

Performance of diffusion gradient in thin films to evaluate the toxic fraction of copper to Daphnia magna.

This study investigates the relevance of the diffusion gradient in thin films technique (DGT) to measure copper's induced lethality on Daphnia magna in natural water spiked with various organic ligands. Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and glycine were used as artificial organic ligands in controlled solutions of mineral water. With EDTA, DGT measurement makes it possible to predict the toxicity of the mixture because Cu-EDTA complexes are inert, whereas DGT is of no help in the case of NTA, because Cu-NTA complexes are fully labile. The Cu-glycine complexes appear as partly labile and toxic. Humic acids as well as fresh and aged algae extracts also were used as models for natural dissolved organic matters. All three of them form copper complexes that are not toxic to Daphnia magna and appear as partly labile with open-pored DGT. However, the use of restricted gels in DGT greatly reduces the contribution of labile complexes, at least for humic acids and aged algae copper complexes. The DGT with restrictive gels, therefore, appears to be a powerful tool for measuring bioavailable copper in natural water bodies, especially when the dissolved organic matter mostly is of humic origin. The DGTs potential ability to mimic the lability induced by the biological uptake also is discussed.

Animals↗

Application of sediment quality guidelines in the assessment and management of contaminated surficial sediments in Port Jackson (Sydney Harbour), Australia.

Sediments in the Port Jackson estuary are polluted by a wide range of toxicants and concentrations are among the highest reported for any major harbor in the world. Sediment quality guidelines (SQGs), developed by the National Oceanographic and Atmospheric Administration (NOAA) in the United States are used to estimate possible adverse biological effects of sedimentary contaminants in Port Jackson to benthic animals. The NOAA guidelines indicate that Pb, Zn, DDD, and DDE are the most likely contaminants to cause adverse biological effects in Port Jackson. On an individual chemical basis, the detrimental effects due to these toxicants may occur over extensive areas of the harbor, i.e., about 40%, 30%, 15% and 50%, respectively. The NOAA SQGs can also be used to estimate the probability of sediment toxicity for contaminant mixtures by determining the number of contaminants exceeding an upper guideline value (effects range medium, or ERM), which predicts probable adverse biological effects. The exceedence approach is used in the current study to estimate the probability of sediment toxicity and to prioritize the harbour in terms of possible adverse effects on sediment-dwelling animals. Approximately 1% of the harbor is mantled with sediment containing more than ten contaminants exceeding their respective ERM concentrations and, based on NOAA data, these sediments have an 80% probability of being toxic. Sediment with six to ten contaminants exceeding their respective ERM guidelines extend over approximately 4% of the harbor and have a 57% probability of toxicity. These areas are located in the landward reaches of embayments in the upper and central harbor in proximity to the most industrialised and urbanized part of the catchment. Sediment in a further 17% of the harbor has between one and five exceedences and has a 32% probability of being toxic. The application of SQGs developed by NOAA has not been tested outside North America, and the validity of using them in Port Jackson has yet to be demonstrated. The screening approach adopted here is to use SQGs to identify contaminants of concern and to determine areas of environmental risk. The practical application and management implications of the results of this investigation are discussed.

Animals↗

Effect of taurine, L-glutamine and L-histidine addition in an amino acid glucose solution on the cellular bioavailability of zinc.

Radioactive zinc was used to study the effect of a binary parenteral nutrient solution, composed of amino acids and glucose, on zinc uptake by fibroblasts. The influence of addition of taurine, L-glutamine and of the increase in L-histidine content of the admixture was assessed. The pure mixture was highly toxic for cells and so it was diluted 1/5 in tyrode buffer with 2% albumin. As compared with cells incubated in the buffer containing albumin, zinc absorption was significantly higher (P < 0.05) in the presence of the amino acids of the mixture. Amino acids thus increased bioavailability by displacing zinc bound to albumin. When the histidine concentration in the nutrient medium (4.2 mM) was doubled, inhibition was noted after 30 min of incubation and zinc uptake thereafter remained comparable to that in histidine-free medium. The addition of glutamine (4.2 mM), usually not present in binary mixtures, resulted in significant differences as compared with glutamine-free control medium. Taurine (0.8 mM), led to a constant increase in zinc uptake by fibroblasts as compared with that obtained with taurine-free mixture. However, ultrafiltration showed that taurine was not able to displace zinc from albumin.

Biological Availability↗