Limit values long-term exposure

There have been a nnmber of estimates of bioconcentration factors for total PCBs in aqnatic species following long-term exposure to PCB mixtures (EHC 140). Values for both invertebrates and hsh have been extremely variable, ranging from values below 1 to many thonsands. Bioaccnmnlation factors for birds and mammals for different Aroclors have indicated only limited degrees of bioaccumulation from food, for example, 6.6 and 14.8 for the whole carcasses of big brown bats Eptesicus fuscus) and white pelican (Pelecanus erythrorhynchos), respectively (see Environmental Health Criteria 140). 

In UK and Finland, the following values are used long-term exposure limit 8h TWA of 100 ppm (560mgm ) and short-term exposure limit of 15min at 150ppm (840mgm ). 

Reliable acute LCso values for death in each species are recorded in Table 2-1 and plotted in Figure 2-1. Acute exposure to high concentrations of 1,1,1-trichloroethane can be lethal to humans and animals. The cause of death is usually either respiratory or cardiac failure. Limited human data and studies in animals indicate that long-term exposure to low or moderate 1,1,1- trichloroethane concentrations may not influence survival. 

The workplace exposure limits are subject to time-weighted averaging. There are two such time-weighted averages (TWA) - the long-term exposure limit (LTEL) or 8 hour reference period and the short-term exposure limit (STEL) or 15 minute reference period. The 8 hour TWA is the maximum exposure allowed over an 8 hour period so that if the exposure period was less than 8 hours the workplace exposure limit is increased accordingly with the proviso that exposure above the LTEL value continues for no longer than 1 hour. 

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