Utvärdering av ett laktest för jordar kontaminerade med ... - Sysav

Abstract
In order to reach the Swedish environmental objective 'A Non-Toxic Environment' there is a
need to make inventories of, and decontaminate, polluted sites. Approximately 80 000
contaminated sites have been identified in Sweden and 16 500 of these are estimated to pose a
large or very large risk to human health or to the environment. Decontamination of polluted
sites is often accompanied by large costs. Therefore it is of great importance that priority is
given to the right areas and that resources are used in an efficient way. Risk assessments of
sites polluted with organic compounds are often based on estimations of the soil solute
concentration from measured total contents of the contaminants in the area. However, this
method has proven to be inadequate. There is therefore a need for reliable experimental
methods describing the equilibrium distribution of organic contaminants between soil
particles and solute in order to make more realistic estimates of the soil solute concentration,
and thus the potential for transport and leaching, of the contaminants in question.
The purpose of this study has been to evaluate the stability and the repeatability of an
experimental method for estimating the leaching potential of soils contaminated with nonvolatile
organic compounds. The method is a column leaching test with recirculation aiming
to determine the equilibrium between solid and liquid phase, and thus the maximal soil solute
concentration in the investigated soil. The method has previously been validated for
determination of leaching potential of soils contaminated with polyaromatic hydrocarbons
(PAHs). In this study one soil contaminated with PAHs and another contaminated with
chlorophenols (CPs), chlorinated diphenyl ethers (PCDEs), polychlorinated dibenzofurans
(PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs) were used.
The results showed that the method is satisfactory in respect of repeatability for determination
of leaching potentials of PAHs and CPs. The repeatability of the method decreased with
increased hydrophobicity of the investigated compounds and was considered unsatisfactory
for PCDEs, PCDFs and PCDDs. The influence of colloidal transport on the leaching of the
chlorinated compounds was investigated and the results showed that the CPs predominantly
were transported in dissolved form. Only 1-3% of the leached CPs were transported bound to
particles. 66-94% of the PCDEs, 77-93% of the PCDFs and 82-99% of the PCDDs were
transported bound to particles. The poor repeatability of the PCDEs, PCDFs and PCDDs is
thought to be caused by contaminant heterogeneity in the soil and on the colloids set in
motion. The method was robust to a 50% increase in flow, from 20 to 30 ml h -1 . No
differences in physical and chemical parameters, flow regimes, leached concentrations or
colloid facilitated transport appeared to be caused by the change in flow. Evaluation of the
contact time showed that the recommended recirculation time of 7 days was not sufficient for
obtaining chemical equilibrium in the system. When increasing the contact time to 22 days the
leached concentrations increased for all PAHs except Naphthalene. The low-chlorinated CPs
appear to reach equilibrium after 7 days, whereas the leached concentrations of the highchlorinated
CPs, above all TeCP, increased with increased contact time. When comparing
experimentally determined leaching with leaching estimated from the total content of the
contaminants in the soil, large differences were observed. The estimated leaching was much
higher than experimentally determined for the most hydrophilic compounds and much lower
for the most hydrophobic. The large differences exemplify the need of a reliable method that
can be used in risk assessments for determination of leaching potential from soils
contaminated with organic compounds. The investigated column leaching test has the
potential to meet this need for PAHs and CPs.
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