Toxicity risks

Toxicity, Risks, and Risk Assessment References 336 Bibliography 344... 

Carbon dioxide and certain halon compounds have a specialized application for fires in electrical equipment where a non-conducting medium is important. All are toxic to a degree, and operate either by smothering the fire or by a chemical reaction which inhibits combustion. Gas extinguishers must not be used in a confined space because of the toxic risk or the risk of asphyxiation. 

Segregation is a common means of controlling toxic risks, or restricting the working area exposed to them. Segregation may be by any or a combination of ... 

SHEEHAN D M (1998) Herbal medicines, phytoestrogens and toxicity risk benefit considerations. Proc Soc Exp Biol Med. 217 (3) 379-85. 

The most difficult problem of risk evaluation linked to chemicals will be discussed in this Part. This is primarily a medical problem, which therefore comes within the competence of the company medical officer and epidemiologists, but neverthel need not only be dealt with by them. The person in charge of safety control in a place where chemicals are handled also has to tackle this problem. This person will have to take into account the level of toxicity risk of a substance. This will determine the constraint level of the measures to be taken, its favoured means of penetration, which depends on the activity, and its penetration properties specific to the organism. The physical properties of the substance (which will determine the nature of the precautions to be taken) and also the values of toxicity parameters have to be taken into account. He has to check the container labelling and know how to interpret and explain the toxicity instructions on this labelling. 

In describing the main parameters used to estimate toxicity, the previous factors will be taken into account for some types of estimates. It will then be seen how difficult it is to interpret these estimates illustrating the difficulties raised by their use. Finally, a possible way of estimating toxic risk parameters will be suggested and applied to a few practical cases, emphasising how cautious one has to be when using it. 

This code is of limited usefulness (see para 1.5.3) (it is supposed to contain in one figure only the level of the three factors inflammability, toxicity and stability). So far as toxicity risk is concerned, the definition of the three degrees is clear and makes it easy to choose between the different risk levels, it is defined by LD50 values (given in mg/kg) and LC50 (given in ppm). 

These degrees are then used by SAX to define toxic risk according to the nature of penetration. So a substance might be hardly toxic by intraperitoneai penetration and moderately toxic when it penetrates subcutaneously . 

These criteria can be used to put forward a hypothesis on the potential toxicity risk level of a substance, which is not listed in labour regulations. The other criteria are either qualitative or take into account biological tests that go beyond the sphere of non-medical staff. It can be interesting to compare LC and LD50 data with clauses concerned with risk offered by the regulations and that appear in our tables. Here are a few examples of common substances, for which there is better information than for the others. 

Problems posed by the determination of toxic risk levels... 

Note that this large range contains the value 930 mg/kg, which comes from another source and would have justified application of code R22. This example thus illustrates the fact that one has to be careful in this particularly serious context of toxicity risk. This approach to estimation by range is another reason why the approach to estimation by regression as seen in paragraph 3.4 should be used. 

From this it can be decided whether it makes sense to identify toxicity risk using LD values determined for a means of penetration different from inhalation, skin or orally. If it does make sense, it will be possible to estimate risk although regulations did not provide any criteria. Note that on top of the space of variables mentioned above it is possible to have in this space bodies , which can be of help in interpreting axes. 

So fares toxicity risk through Inhalation is concerned, which is the most common under normal working conditions, a quantitative index of toxicity is suggested on p.140. 

In the past, mineral oil hydraulic fluids sometimes included additives such as polychlorinated biphenyls (PCBs) to improve the thermal resistance or other properties of the resulting fluids. These additives may present more toxicity risks than the primary ingredients of the hydraulic fluids. While such uses of PCBs have been discontinued, PCBs may be encountered as components of hydraulic fluids at NPL sites contaminated by hydraulic fluids (ATSDR 1993b). 

Obtaining a good quality QSAR model depends on many factors, such as the quality of biological data and the choice of descriptors and statistical methods. As a consequence, the uncertainty of the QSAR predictions is a combination of experimental uncertainties and model uncertainties. QSAR methods have to be applied to individual chemicals, not on mixtures. If the QSAR demands it, the components of the mixture have to be addressed separately and individually - in case of unknown compounds, QSAR cannot identify the toxicity risk and is therefore not useful. 

Five recent studies investigated the potential toxic risk if CNTs reach the pleural cavity after inhalation exposure [6,88-91]. Three of these in vivo studies revealed that if CNTs are delivered to the abdominal cavity of mice or rats, they could induce a serious potential carcinogenic risk resembling that associated with exposure to certain asbestos fibers [6,88,89]. The other two studies described nontoxic responses [90,91]. 

FIGURE 8.9. Flowchart A. Overall decision tree for evaluation on repro/developmental toxicity risk from Wedge Document, 1999, distributed through www.FDA.gov (June, 1999). 

Fabro, S., Shull, G. and Brown, N.A. (1982). The relative teratogenic index and teratogenic potency Proposed components of developmental toxicity risk assessment. Teratog. Carci-... 

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