Exposure assessments sampling issues

An important issue related to evaluating health effects of PCBs in humans is exposure assessment. Exposure to PCBs has been assessed by measuring PCBs in blood, breast milk, and adipose hssue. Umbilical cord blood also has been used to estimate exposure in utero. In addition, fish consumption has been utilized as surrogate of PCB exposure in some studies, but this measure of exposure has not always been reliable. Mean serum PCB levels range from 0.9-1.5 ppb (pg/L), in recent years, in individuals who do not have diets high in fish from waters contaminated with PCBs. In the absence of human data, environmental sampling (soil, sediment, air, food, water) has also been used to estimate exposure. 

Airborne solvent concentrations usually vary much with time. Although repeated random personal sampling is theoretically the optimal method for inhalation exposure assessment, it is very time-consuming and does not necessarily reveal the reasons for exposure. Often, occupational hygiene surveys are conducted only to make certain that the concentrations of air impurities are in compliance with flic OELs. Also, the European standard (EN 689/95) for occupational exposure assessment is primarily issued for this purpose. It would, however, be practical if the measurements conducted would also provide useful information for planning of remedial measures if flic measurements reveal those to be necessary. For this purpose, it is important to recognize flic difference between manual tasks and process industries. 

In addition to the studies on the trends of POP levels in the environmental samples, time trends of human exposure is also an important issue for understanding the long-term toxic impacts on general population. Minh et al. (2004) assessed the decline in the rate of human exposure to DDTs and PCBs over the 10 years period (1989 and 2001). A first-order kinetic approach was used to estimate the declining rate of DDTs and PCBs in human breast milk collected from Vietnam. The decrease in the POPs such as DDTs, PCBs, and HCHs in human breast milk was suggested to follow first-order kinetic (Noren Meironyte, 2000). Another important factor for the assessment is the half-life (Aieci, 2) defined as the duration in which initial concentrations decrease to a half. On the basis of the residue concentrations of OCs in 1989 reported by Schecter et al. (1989a) and the levels in 2001 obtained by Minh et al. (2004), the rate constant and tdeci/2 were estimated. 

It is also evident from Table 6 that cosmogenic nuclide production rates should be determined for more compositions of target elements. Though not all minerals are likewise suited for surface exposure dating with He and Ne (see Experimental issues below), there are certainly more than just olivine and quartz. And finally, a determination of the contribution to He and Ne production from muon-induced reactions would be important to assess exposure histories of samples from shielded locations or where erosion is high. 

Risks to persons or to the environment must be minimized by adherence to safety legislation and protocols, e.g., Occupational Health and Safety (COSSH in the UK), which informs on health risks associated with specific chemicals and appropriate medical and cleanup procedures in the event of exposure or a spillage. Before undertaking field work, a site-specific risk assessment should be carried out to identify potential risks and specify safe practices. Important issues include transport of persoimel and equipment, weather conditions, possible health risks from the sample and the general environment, appropriate protective clothing, safe onsite working practices, safe use of equipment, communications, and emergency procedures. 

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