By-products or contaminants :: terrestrial ecosystems

Key concerns:

There is a paucity of data on the effects of PAHs on species indicative many terrestrial ecosystems. Some PAHs are known or suspected carcinogens, although the ecological consequences have not been established, as most organisms will be predated before they develop carcinomas. However tumours in fish can present a problem for the human food chain. 

Ecosystem specific information

Arable - PAHs have been shown to be taken up by various fruit and vegetables grown in various soils contaminated with PAHs The crops studied included lettuce, potato, carrot, radish, green bean, squash, pear, apple, plum, elderberry, blackberry, gooseberry, blackcurrant, redcurrant, hip and hazelnut. The concentrations of PAHs in the crops ranged from not detected to 3 µg/kg wet weight, and were not correlated with the concentration in the soil (Samsoe-Petersen et al. 2002).

Airborne PAHs may be taken up by various species of plants, including corn (Zea mays) and sunflower (Helianthus annuus). PAHs detected include phenanthrene, fluoranthene, pyrene, triphenylene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, Indeno(c,d)pyrene, benzo(g,h,I)perylene, dibenzo(a,h)anthracene and coronene. Concentrations of individual compounds in the leaves of corn and sunflower ranged from 0.22 to 8.6 and 1.49 to 110 µg/kg dry weight, respectively (Bohme et al. 1999). 

Bogs, wetlands and heath - Analysis of peat cores sampled from an ombrotrophic bog in a rural area in north west England has shown that the maximum loading of PAHs up to the 1930s, with subsequent reductions following the introduction of emission controls (Sanders et al. 1995). Similar data is available for an ombrotrophic bog in Switzerland (Berset et al. 2001).

Coastal and rocky habitats - PAHs are acutely toxic to aquatic organisms due to the formation of toxic metabolites. The PAHs which are most toxic to algae are benz(a)anthracene and benzo(a)pyrene, with EC50 values ranging from 1 to 29 µg/l and 5 to 15 µg/l, respectively (WHO 1998). Corresponding EC50 values for 3 ring PAHs range from 240 to 940 µg/l. Naphthalene is less toxic than other PAHs, with EC50 values in algae ranging from 2800 to 34 000 µg/l.

PAHs have been shown to be toxic to various taxonomic groups of invertebrates, including crustaceans, insects, molluscs, polychaetes and echinoderms. No clear difference in sensitivity between these groups was reported. Toxicity of five PAHs to polychaete worms ranged from 300 to 3800 µg/l. Of the PAHs tested, 1-methylphenanthrene was the most toxic, and naphthalene the least toxic (Rossi & Neff, 1978). An LC50 value was not reported for chrysene, but the corresponding NOEC was >1000 µg/l. An EC50 for effects on the feeding rate of the mussel (Mytilus edulis) was 80 µg fluoranthene /l (Dunkin et al (1989). Three-hour LC50 values for brine shrimp (Artemia salina) were 8, 20 and 40 µg/l, for pyrene, anthracene and fluoranthene, respectively (Kagan et al 1985) .

There is a paucity of LC50 data for marine fish, although Winkler et al (1983) reported a NOEC, with reference to hatching success, of 7.0 µg/l for California grunion (Leuresthes tenuis) embryos exposed to benzo(a)pyrene for 14 days. A 5 day EC50 of 0.1 µg/l was reported for flatfish (Psettichtys melanostictus) exposed to benzo(a)pyrene (Hose et al 1982)

Grassland - Grassland sites close to industrial areas, with chemical and steel industries, or major highways have been shown to be contaminated with PAHs (Weiss et al. 1994; Tuhackova et al. 2001).

Concentrations of the sum of 18 PAHs in soil adjacent to industrial sites ranged from 0.28 to 79.0 mg/kg, and were not correlated with either locationor the presence of other contaminants. The PAHs measured were acenaphthylene, acenaphthene, fluorine, phenanthrene, anthracene, fluoranthene, pyrene, triphenylene, benzo(a)anthracene, chrysene, benzo(e)pyrene, benzo(b)fluoranthene, benazo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, benzo(g,h,I)perylene, indeno(1,2,3-c,d)-pyrene and coronene.

PAH concentrations were related to the distance from the source, demonstrating a biphasic character which can be interpreted as bimodal distribution of exhaust microparticles with different rates of deposition. PAHs such as benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene and indeno(1,2,3-cd)pyrene decreased with increasing distance from the road, whereas phenanthrene, fluoranthene, pyreneand benzo(a)pyrene and benzo(g,h,i)perylene tend not to show such a concentration gradient, as they tend to found on the lighter particle fraction (Tuhackova et al. 2001).

Airborne PAHs may be taken up by various species of grassland plants. PAHs detected include phenanthrene, fluoranthene, pyrene, triphenylene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, indeno(c,d)pyrene, benzo(g,h,I)perylene, dibenzo(a,h)anthracene and coronene. Mean concentrations (µg/kg dry weight) of individual compounds were as follows: ryegrass (Lolium sp.),0.187-5.8; thistle (Cirsium arvense), 0.31-12.7; dandelion (Taraxacum officinale) 0.23-11.9, ribwort (Plantago lanceolata), 0.61-9.4 yarrow (Achillea millefolium), 0.20-48 lady's mantle (Alchemilla vulgaris), 0.43-16.1; autumn hawkbit (Leontodon autumnalis) 0.117-8.5, and white clover (Trifolium repensi), 0.151-22 (Bohme et al. 1999).

Woodlands and hedgerow - PAHs can be adsorbed by spruce needles (Brorstrom-Lunden and Lofgren 1998), tree bark (Douce et al. 1997) and the leaves of deciduous (Howsam et al. 2000b; Howsam et al. 2000a; Howsam et al. 2001b; Howsam et al. 2001a) and evergreen (Alfani et al. 2001; Muller et al. 2001) trees.

Concentrations of PAHs in soil from a deciduous woodland were higher than corresponding concentrations in adjacent pasture (Howsam et al. 2000b), indicating increased deposition from leaf litter, stem-flow and/or through-fall.

Concentrations of PAHs in the leaves of oak, ash and hazel trees were correlated with concentrations in the atmosphere, although uptake by the leaves while they were on the tree was generally low (Howsam et al. 2001a). Oak and ash had similar PAH profiles, whereas hazel leaves had a proportionally increased concentration of the heavier PAH compounds (Howsam et al. 2001b). Concentrations were also affected by biological parameters, with leaves exhibiting pubescence having higher PAH concentrations than those which were hairless (Howsam et al. 2000a).

PAH concentrations in the leaves of the evergrren Mediterranean oak (Quercus ilex L.) varied according to local sources, with low molecular weight compounds prevalent in control sites, with fluoranthene, pyrene and benzo[a]anthracene dominant in areas close to major roads (Alfani et al. 2001).