Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 400

9.8.2 Gasoline Contaminants

Gasoline is a mixture of light petroleum products (for example alkanes such as hex-
ane, and aromates such as benzene and toluene) plus additives like ethanol and
MTBE. They frequently occur in the groundwater due to leaching storage tanks.
Gasoline contaminants are volatile and usually rapidly degraded. Thus, concentra-
tions in aerated soil are generally low (Fig. 9.7 ). Accumulation in crops from soil
has not been described, except in laboratory experiments. An exception is MTBE,
which is less volatile and more persistent. MTBE was not metabolized in any of
24 plant species tested (Trapp et al. 2003 ). Uptake of benzene from air is rapid but
levels are low, due to a low K OA , and insignificant for human exposure (Collins et al.
2000 ).

9.8.3 Heavy Petroleum Products

The heavy fraction of petroleum products consists of long-chain alkanes and some
polycyclic aromatic hydrocarbons. These contaminants are lipophilic, volatile and
degradable under aerobic conditions. Significant uptake from soil into plants has not
been observed and is not expected from the properties of petroleum components.

9.8.4 Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) is a group of contaminants with two
(naphthalene) to seven or more condensed aromatic rings with wide-spread occur-
rence in the environment from incomplete combustion. Most of these contaminants
are very lipophilic (log K OW 5

7) and have a very low water-solubility. Uptake
into plants with transpiration water is therefore unlikely. Contamination of plants is
mainly via attached soil particles or from air (Delschen et al. 1999 ). Uptake from soil
into the peel of carrots or potatoes may occur. Solubilization by cucurbita species
(pumpkin and zucchini) is likely.

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9.8.5 Persistent Organic Pollutants POPs

Persistent Organic Pollutants (POPs) are chlorinated contaminants like the pesti-
cides DDT, dieldrin and lindane, but also polychlorinated biphenyls (PCB) and
polychlorinated dibenzo- p -dioxins and -furans (PCDD/F). POPs are persistent,
semi-volatile and lipophilic. Similar to PAHs, the uptake with transpiration water
into plants is very unlikely, while attached soil particles can lead to contamination of
plants. Solubilization with subsequent translocation by cucurbita species (pumpkin
and zucchini) has been observed repeatedly.

9.8.6 Explosives

Explosives such as trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine
(RDX) are relatively polar contaminants with low vapor pressure. High uptake into