Summary and conclusions

Fytoremediering - Danske forsøgsoprensninger og international litteraturgennemgang.

Successful phytoremediation at field scale, i.e. clean-up of soil to clean-up standards by using vegetation, has not been reported. There have only been partial successes, e.g., improvement of degradation rates or reduced final concentrations. The same is true for the majority of laboratory studies.

From 1999 to 2006, the Danish EPA supported three field-scale phytoremediation tests using willow and poplar on sites contaminated with petroleum and coaltar products.

It took three growth seasons to establish a vegetation cover on all three sites . Numerous trees had to be replanted, not because of soil toxicity, but because of agronomic problems like water stress, over-fertilization or lack of weeding.

One of the conclusions of the tests is that phytoremediation using non-crop plants is safe for use on public land. Plant shoots did not contain toxic organic compounds. However, in case of significant soil contamination with heavy metals, plant shoots should be checked for heavy metals.

In Denmark, willow and poplar can be used to accelerate the degradation of petroleum hydrocarbons, naphthalene and BTEX in the vadose zone and in the zone of a fluctuating water table. Degradation is estimated to be of the order of 0.2 kg hydrocarbons per square metre and year. However, phytoremediation is not usable for PAHs, NSO-substituted PAHs, DEHP, NPE and LAS.

Based on the existing knowledge from field experiments, it is not possible to estimate the time required for meeting clean-up goals using phytoremediation. However, a timescale of up to 10 years seems to be too short.

It can be concluded that at present, phytoremediation cannot be recommended as a clean-up technology in Denmark, because the time required for meeting clean-up goals is too uncertain and most likely not acceptable for site owners. However, if the owners opt to commit their land until further notice to growing renewable energy using willow or poplar, then phytoremediation or phytostabilisation can be a meaningful option with a very long-term clean-up goal. In the meantime, environmental and human exposure to soil contamination will be minimised as an effect of the vegetation.