Industrial chemical groupings :: terrestrial ecosystems

Key Concerns:

The use of PCBs has been progressively restricted in the UK since the 1970s, and in 1986 their sale and use in new plant and equipment was banned. Many PCBs are highly resistant to degradation or metabolism, they are readily bioaccumulated, and they continue to persist in the environment, several decades after their use was initially restricted. Although levels are lower compared to the 1960s, PCBs are still released to the atmosphere through cycling from environmental processes (Meijer et al. 2002). PCBs have recently been identified in air sampled from hazardous waste sites (WHO 1993; Ruokojarvi et al. 1995; Eisler 1996; ATSDR 2000).

Ecosystem specific information

Arable habitats - Inhibition of the growth of soybean (Glycine max) and fescue (Fescue arundinacea) have been reported following soil application of Aroclor 1254 at 1000 mg/kg. No significant effects on growth were reported at lower application rates, although a dose-related decrease in uptake of water by the soybean was also noted (Weber and Mrozek 1979). Similar effects have also been found in beet (Beta vulgaris), exposed to 1000 mg/kg but not in corn (Zea mays) or sorghum (Sorghum bicolour) (Strek et al. 1981).

Bogs, wetland and heath - There is a paucity of data on the effects of PCBs on species indicative of bog, wetland or heathland ecosystems.

Analysis of peat cores demonstrated maximum PCB inputs during 1964, although by 1976 this had declined by 65% (Sanders et al. 1995). Peat from the top of the core, representing current times, showed an increase in net PCB flux. This is due to various factors, including upward migration / outgassing from deeper in the core, an artefact from surface vegetation and current atmospherically derived burdens entering the natural environment.

Coastal and rocky habitats - The toxicity of PCBs to saltwater invertebrates is variable, even between closely related species. Toxicity is related to the degree of chlorination, although this is not a direct correlation, as the most toxic congers are often those in the mid-range of chlorination (WHO 1993). Acute LC50 values range from 0.01 to >10 mg/l (Portmann and Wilson 1971; Mayer 1987).

The toxicity of PCBs to freshwater fish also varies between species and PCB mixtures. Test conditions, such as the temperature and hardness of the water do not strongly influence toxicity. Acute LC50 values for Harlequin fish (Rasbora heteromorpha) exposed to various PCB mixtures ranged from 0.32 to >100 mg/l (Tooby et al. 1975). LC50 values for salmonid species ranged from 0.13 to 60.9 (Mayer and Ellersieck 1986).

PCBs have been shown to impair reproduction in seals following the consumption of contaminated fish. This has been noted in both field and laboratory studies (WHO 1993).

Grasslands - There is a paucity of data on the effects of PCBs on species indicative of a grassland ecosystem.

PCBs is the atmosphere will be absorbed by and eliminated from plant species such as ryegrass (Lolium multiflorum) (Komp and McLachlan 2000). For many PCB congeners, complete elimination witin 240 hours was reported, suggesting that the partitioning of PCBs from the gas phase into ryegrass was reversible. Grassland species such as reed canarygrass (Phalaris arundinacea L.) and switchgrass (Panicum variegatum) have been shown to dissipate PCBs in soil. After six month exposure, 51% or less of an initial PCB soil concentration of 100 mg/kg remained in the soil (Kudjo-Dzantor et al. 2000). Other plants such as tall fescue (Festuca arundinacea Schreb) and deertongue (Panicum clandestinum) were less able to stimulate dissipation of PCBs.

Woodland and hedgerows - There is a paucity of data on the effects of PCBs on species indicative of woodland or hedgerow ecosystems.

PCBs have been detected in the needles of coniferous trees, although generally at low (µg/kg) concentrations. Higher concentrations may indicate recent input of these pollutants (Herceg-Romanic 2002). The concentration of total PCBs in white spruce (Picea glauca) needles from trees growing adjacent to a hazardous waste incinerator decreased with increasing distance from the incinerator (Blais et al. 2003). Trees growing within 5km of the incinerator had concentrations up to 128 µg/kg wet weight, although these concentrations are due to an accidental release of PCBs from the plant 6 months earlier. Concentrations in trees growing within 5 to 10 km of the plant were 2 to 10 µg/kg. Needles sampled one year after the initial analyses had concentrations up to 70 µg/kg (within 5km of the palnt) and 0.2 to 1 µg/kg (5 to 10 km from plant). The pattern of PCB congeners was also correlated with distance from the plant with the heavier congeners dominating at the sampling sites closest to the plants. The heavier congeners also have higher octanol-water partition coefficients, and therefore have a greater tendency to condense out of the gas phase (Blais et al. 2003). The effects of the PCB release on the vegetation were not studied.