Health risks concentration levels

As discussed in Chapter 4, chemicals can be a nuisance or pose health risks if they become airborne as a result of inadequate process control, operation and maintenance malpractice, inadequate maintenance, incomplete understanding of the process etc. Hazards may arise if the oxygen concentration in the air fluctuates beyond its normal level of 21% by volume, and fire/explosion dangers may arise from the presence of flammable gases, vapours or dusts in the atmosphere. Thus air quality tests may be required for a variety of purposes such as ... 

If linear (dose) models without thresholds are to be used for carcinogen (or other) risk assessment, estimation of exposure at specified levels becomes irrelevant to risk assessment or, at least, its use is nonintuitive. For example, a carcinogen risk analysis may be based on a linear, nonthreshold health effects model. The total health risk would thus be proportional to the long-term exposure summed for all affected people for the identified period, and exposure of many people at low concentrations would be equivalent to exposure of a few to high concentrations. The atmospheric dispersion that reduces concentrations would also lead to exposure of more people therefore, increments... 

Accordingly, the total petroleum hydrocarbons at a gasoline spill site will be comprised of mostly Cs to Cu compounds, while total petroleum hydrocarbons at an older site where the fuel has weathered will likely measure mostly Cg to Cn compounds. Because of this inherent variability in the method and the analyte, it is currently not possible to directly relate potential enviromnental or health risks with concentrations of total petroleum hydrocarbons. The relative mobility or toxicity of contaminants represented by total petroleum hydrocarbons analyses at one site may be completely different from that of another site (e.g., Ce to Cn compared to Cio to C25). There is no easy way to determine if total petroleum hydrocarbons from the former site will represent the same level of risk as an equal measure of the total petroleum hydrocarbons from the latter. For these reasons it is clear that the total petroleum hydrocarbons value offers limited benefits as an indicator measure for cleanup criteria. Its current widespread use as a soil cleanup criterion is a function of a lack of understanding of its proper application and... 

O2 concentrations, such as found in marine wetlands. High biomethylation rates have also been observed in coastal sediments. Because methylmercury is transferred up the food chain, the marine fish that occupy high trophic levels have very high mercury concentrations. In some cases, such as for tuna and swordfish, concentrations are high enough to pose human health risks. 

STEL Short Term Exposure Limit (STEL) refers to a safe level of exposure (see also TLV) from inhalation tor a continuous period of time that is short (by OSHA standards either a 15 minutes or 5 minutes of continuous exposure). The concentration established by the STEL (usually in ppm) should not be exceeded during that period of exposure, and further, the time limit of continuous exposure should not be exceeded, else there is a health risk. 

The goal of occupational toxicology is to ensure work practices that do not entail any unnecessary health risks. To do this, it is necessary to define suitable permissible levels of exposure to industrial chemicals, using the results of animal studies and epidemiological studies. These levels can be expressed by the following terms for allowable concentrations. 

In 2001, the French Toxicity Research Commission on Pesticide Products cited conclusions by IARC, USEPA, and EU that atrazine is not carcinogenic to humans (French Republic Ministry of Agriculture, 2001). The Commission further stated, Considering all these factors, the concentration of the triazines in water, even elevated levels identified in the field both in transitory and localized form, do not represent a public health risk. ... 

The oral reference dose (Oral RfD) is an estimate of the daily exposure of a person to a contaminant that is likely to be without appreciable risk of a deleterious non-carcinogenic effect during a lifetime (USEPA http //www.epa.gov/iris/). Oral RfD values for POP concentrations in seafood types are presented in Table 16.5, together with the daily intake of POPs from seafood consumed in Singapore. Daily intakes of POPs from seafood are below the oral RfD. The cancer benchmark concentration (Dougherty et al., 2000) represents the exposure concentration at which a lifetime cancer risk equates to one excess cancer death in one million persons. This level is defined as the public health protective concentration in the Congressional House Report to the Food Quality Protection Act of 1996 in the USA. Cancer benchmark concentrations were exceeded for DDTs, heptachlor, and PCBs (See Table 16.5). The cancer hazard ratio is the ratio of the MDI for a specific contaminant relative to the cancer benchmark concentration. The cancer hazard ratio represents the extent to which average daily exposure exceeds the benchmark concentration. The cancer hazard ratio of seafood consumption... 

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