Benzene, Toluene, Ethyl Benzene and
Xylene (BTEX) are the volatile components commonly associated with
petroleum products. Most petroleum contaminated sites are located
within modified environments, and the primary requirements for
ecological protection relate to the protection of off-site environment
quality and to the associated ecosystems.
In New Zealand, soil
acceptance criteria have been developed for BTEX, representative
polyaromatic hydrocarbons (PAHs); pyrene and benzo-a-pyrene, and total
petroleum hydrocarbons (TPH), based on the protection of human health
and have been derived for a number of land uses, soil types and depth of
contamination (MfE, 1999).
Asthetic impact, protection of terrestrial
ecosystems and protection of groundwater quality have not been
considered in the derivation of these criteria and need to be addressed
on a site-specific basis. Thresholds for the protection for groundwater
quality are given as separate soil acceptance criteria in these
guidelines to help evaluate future off-site impacts.
Efforts to establish soil criteria for
petroleum hydrocarbons in soil are complicated by a number of variables
such as the:
altered toxicity of aged
role of the oil
phase in altering bioavailability
lack of information on
bioaccumulation of particular constituents
dependence on uptake by
biota and toxicity on soil characteristics
uncertainty in ecotoxicity of different constituents of petroleum
presence of co-contaminants at field locations where
adverse ecological impacts may be observed (Efroymson, 2000).
like Canada are developing a nation-wide standard for petroleum
hydrocarbons which will contain action levels for soil contaminants.
This standard was not available at the time of publication.
There are very few studies reported in
the international literature on the ecological impacts of BTEX compounds
to soil flora and fauna. Mostly, BTEX is volatilised from the surface of
the soil after a spill, and these monoaromatic hydrocarbons are thought
to be primarily a human health concern. Risks to groundwater is
considered the next most important due to the high relative mobility of
BTEX through soils.
We conducted some pilot studies to
determine ecotoxicoity values for BTEX to soil invertebrates and plants
using standardised methodologies. However under the standardised
conditions prescribed by the testing methodologies we were unable to
obtain consistent soil concentrations, as these compounds were rapidly
volatilised from the test soil. For example, soil samples individually
spiked with 2000 ppm of xylene,ethylbenzene or toluene, showed the
following losses with time:
Xylene: after 30 minutes - up to
50% loss, after 6 hrs in an open test vessel up to 89% loss
Ethylbenzene: after 30 minutes -
up tp 65% losss, after 6 hours in an open test vessel up to 98% loss
Toluene: after 30 minutes - up to
83% loss, after 6 hours in an open test vessel up to 99% loss.
These results are in accordance with
Salanitro and colleagues who report that 40 - 95% of BTEX hydrocarbons
applied to a soil sample were volatilised during the soil preparation
process (Salanitro et al., 1997). Therefore, unless
volatilisation can be contained or prevented, it is difficult to define
consistent toxicity relationships between BTE and X and the fauna and
flora inhabiting the topsoil. Currrently, such conditions contravene the
prescribed moisture conditions for invertebrate or plant culture. Until
more sophisticated standards and systems for testing monoaromatics are
designed, we beleive that the derivation of ecological tolerance levels
for BTEX as stand alone compounds is largely unachievable.
Efroymson, E 2000 Contaminated Soils
Advisory Group. SETAC Globe 1 (2):57.
MfE, 1999: Ministry for the
Environment - Guidelines for assessing and managing petroleum
hydrocarbon contaminated sites in New Zealand. Module 4 - Tier 1 Soil
Salanitro, J. P., Dorn, P. B.,
Huesemann, M. H., Moore, K. O., Rhodes, I. A., Rice J., L.M., Vipond,T.
E., Western, M. M., Wisniewski, H. L. 1997: Crude oil hydrocarbon
bioremediation and soil ecotoxicity assessment. Environ.Sci.Technol.