Multiple sources of exposure

The limited EU guidance on risk assessment of chemical mixtures does not mean that the issue is not addressed by the EU member states. However, the level of detail and the status of the guidance vary considerably between the member states and the different policy areas. The UK Food Standards Agency established a special working group to formulate advice on risk assessment of multiple residues of pesticides and veterinary medicines in food, and of multiple sources of exposure to these... 

A product lifecycle ranges from resource extraction through manufacture to use and final waste disposal or processing. Under the current EU chemical risk assessment procedure, lifecycle thinking considers the risks at each stage of a substance s lifecycle, with the possible summation of multiple sources of exposures to a single substance [144], LCA that quantitatively evaluate the overall environmental and health impacts of processes, services or products can complement risk assessment as a useful decision-support tool for chemical risk management [183, 188, 536]. 

Until recently, most risk assessments focused on a single pesticide, considered each route separately, and evaluated each separately. Aggregate assessments consider a single pesticide but combine multiple routes and multiple sources of exposure. Cumulative assessments combine exposure assessments for chemicals that share a common mechanism of toxicity. 

This is so far simple, but there are complicating factors. First, drinking water will not be the only source of mercury exposure some gets to people through certain foods, for example. So if the amount present in and taken in from other media is not considered, then the ADI could be exceeded if the drinking water level of 0.01 mg/1 is accepted. The problem of multiple sources of exposure to the same chemical can be much more complex than is suggested in this example, but can not be ignored if the ADI/RfD is not to be exceeded. 

If, unusually, we can demonstrate a connection between a particular chemical and an incident of disease, how do we know which particular exposure to that chemical, and thus which particular source, was responsible This is the problem of multiple sources for any one particular chemical there are usually many sources of exposure, but only by identifying the source that has caused my disease can I identify the human conduct that has caused it, and which therefore is responsible for it. 

As sediments act as pollutant sinks in aquatic systems, they can be important sources of exposure, and so of the entry of chemicals into aquatic food chains. Sediments are the ultimate residence location for many pollutants released to water. The widespread presence of complex mixtures of contaminants in sediment is thus likely to occur in any location where multiple localized and diffuse contaminant sources contribute to the overall chemical load within natural waters. The role of sediment in the receipt and resupply of the chemical to the water phase means that there is interest in monitoring sediment chemical pollutant load over both different spatial and temporal scales. Because the process of sediment deposition and chemical adsorption on the one hand and solubilization and resuspension on the other link the pollutant loads of the sediment and water column, many of the species that can be used to sample the environment for waterborne pollutants (e.g., filter feeders such as mussels) can also describe the pollutant load present in sediments (Baumard et al. 1998). 

Exposure assessments generally focus on a single chemical and a single route of exposure. However, there have been recent efforts to examine multiple pathways of exposure. The current approach is to add the single point estimates for each exposure source to arrive at a sum. Research continues on developing new data and exposure models for estimating multiple-pathway exposures. 

Aggregate exposure (multiple pesticides) The sum of exposures to pesticide chemical residues with a common mechanism of toxicity from multiple sources and multiple routes of exposure (Food Quality Protection Act, 1996) (USEPA, 1997a). 

Biomarkers are often used in test batteries to evaluate the effects of exposure to multiple sources of contaminants and to detect responses to various sources of pollution, such as harbours, miscellaneous industrial sites and municipal and hospital wastewaters. Field studies with biomarkers are often plagued by various constraints, such as spatial variation (e.g. change in habitat characteristics), temporal variation (e.g. cycle of reproduction) and availability of organisms that can hamper data acquisition and prevent the use of multivariate methods during... 

Table 3-6 distinguishes between correlational evidence from field observations and experimental evidence. Correlational evidence from field studies inherently has multiple sources of uncertainty, many of which are controlled in experimental studies. Observations that indicate a positive relation between environmental PCB exposure (sometimes represented by PCB concentration in tissue) and an adverse health effect in free-ranging wildlife are represented in Table 3-6 as correlational field observations. Effects that were observed in experimental studies under controlled or closely monitored exposure conditions were included in the table as experimental observations. However, no entry was made in Table 3-6 for responses that were reported in an experimental study to be equivocal, ambiguous, or not statistically significant. 

The Techa River population exposed to chronic combined external gamma radiation and internal radiation due to 90Sr and 137Cs exhibited alterations in hematological parameters, including leukopenia, thrombocytopenia, and granulocytopenia (Akleyev et al. 1995). These effects were observed in a portion of the exposed population that received radiation doses to the bone marrow at rates in excess of 30-50 rem (0.3-0.5 Sv) per year. These data are omitted from Table 3-3 because exposures were to multiple sources of radiation. 

Figure 4 An Illustration of the Imract of Multiple Sources of Variability on the Overall Distribution of the Estimated Safe Exposure Level. (Data are from Portier and Kaplan, 1 89.)...

U.S. tolerances is the responsibility of the U.S. Food and Drug Administration (FDA). In the absence of a specific tolerance, residues must be below detectable levels. Based on modifications to FFDCA mandated by the Food Quality Protection Act (FQPA) of 1996, several new elements were introduced to the EPA tolerance process. These include the need to consider the special sensitivity of infants and children, the potential exposure via multiple routes of exposure (i.e., aggregate exposure from dietary and non-dietary sources), and the potential for exposure to other pesticides and chemicals with a common mechanism of toxicity (i.e., cumulative exposure). Under FQPA, the EPA was also required to complete a reevaluation of all existing tolerances during a 10-year period. Domestically established M RLs apply also to imported commodities, but there is an established (if somewhat slow) process for evaluation of residue data from other countries in support of import tolerances. 

In Southeast Asia during the 1970s, symptoms began within minutes after an exploding munition (air-to-surface rocket, aerial bomb, cylinder) caused a yellow, oily, droplet mist to fall on individuals within 100 m of the explosion site. The falling droplet rain was inhaled, swallowed, and collected on skin and clothing contaminated the terrain and food and water supply and caused humans and animals to become acutely ill and to die after a variable period.7 Massive cutaneous contact was prevalent when the sources of exposure were sprays or coarse mists that were used deliberately to contaminate humans and the environment. Although the suspected trichothecene mycotoxin attacks in Southeast Asia would have involved multiple routes of exposure, we can postulate that the skin would have been the major site for deposition of a aerosol spray or coarse mist. 

Several additional models have been developed to describe the relationship between air and BLLs. Their general form aeeounts for multiple sources of lead exposure and follows this relationship ... 

In general, the reference standards identify which exposures are allowed or what knowledgeable people recommend. Decisions on acmal exposures will want to consider multiple sources of reference standards and understand how they come about and when they were set. 

Sometimes, even when a meticulous clinical history is taken, the source of exposure remains unidentified. This can be due to multiple causes the exposure can be indirect (produced through a contaminated item). 

Mahaffey If translation is your only source of data, then perhaps that s what you have to do, but there are distinct tissue distributions, metabolic and biological effects for a specific level of metals in tissues that differ for adults and children. Also there are differences in the multiple routes of exposure. One should translate the data only when there s nothing else to do, and I think we probably have more choices than that. 

Each of these potential pathways has multiple sources of lead contamination. The actual lead exposure experienced by any individual varies greatly depending on many specific iactors. Because there are multiple sources and pathways of lead exposure, no single source accounts for the occurrence of elevated blood lead levels in children. 

Exposure and development must be predictable and repeatable because multiple pieces of film may be used for a single plate exposure. The proper exposure source and the intensity of that source must be estabUshed. The imagesetter must be properly linearized to produce the desired precise halftone dots. This film must be handled under correct safelight conditions and machine-processed in chemical developers at the correct speed and temperature. 

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