Soil test

Details Soil test Soil test

2000-06-22

2003-07-29

Soderquist, Arlen (Department: 1743)

Chemistry: analytical and immunological testing

Geochemical, geological, or geothermal exploration

C436S031000, C436S060000, C436S124000, C436S125000, C436S126000, C436S139000, C436S140000, C436S141000, C436S142000, C436S145000, C436S177000, C436S178000

Reexamination Certificate

active

06599747

ABSTRACT:

The present invention relates to a test for the analysis of soil, sand, clay and other earth materials (all collectively referred to herein as “soil” for convenience) contaminated with persistent organic pollutants to determine the bioavailable fraction of the pollutant in the soil, particularly but not exclusively for the purposes of deciding whether or not the soil may be purified using a bioremediation strategy.
Various industrial processes may result in contamination of soil with persistent organic pollutants, e.g. polycyclic aromatic hydrocarbons. Examples of industrial processes resulting in such pollution include incineration processes, wood treatment sites, gas works and power stations. It is obviously desirable, for environmental reasons, that such soil be purified. One such strategy for purification is bioremediation in which the soil may be treated by composting, air-sparging or bioaugmentation or by means of a pump and treat procedure or by using a bioreactor so that organisms proliferating in the soil are able to “digest” the pollutants. However the success or otherwise of a bioremediation strategy depends on the bioavailability of the pollutants in the soil. In other words, only a certain fraction (i.e. the bioavailable fraction) of the pollutants in the soil will be removed by the bioremediation strategy. If this fraction is relatively low then the bioremediation technique, whilst reducing the total level of organic pollutants, may not necessary bring the level down below that required by legislation.
The bioavailability of a persistent organic pollutant in soil is dependent on a number of factors. For example, it has been observed that, as the length of time an organic compound remains in contact with soil increases, the ability for that compound to be degraded by micro-organisms decreases (Hatzinger and Alexander, 1995). The rate at which degradation occurs also decreases (Hatzinger and Alexander, 1995). Similarly, a decrease in solvent extractability has been observed as compound/soil contact time increases (Hatzinger and Alexander, 1995; Kelsy et al, 1997). This decrease in compound availability, with time, has been termed “ageing”. It is the rapidly desorbed fraction which equates to the bioavailable fraction (Cornelissen 1998).
The nature and extent of ageing is dependent upon soil structure, intra-soil processes and the compound's intrinsic properties. Fundamental parameters include (Brusscau et al. 1991; Jones et al, 1996): aqueous solubility, vapour pressure and octaonol: water partition coefficient (Kow). It has been proposed that ageing is the amalgamation of a number of intra-soil process including: sorption onto soil particles (Ball and Roberts, 1991a; Fu et al, 1994; Burgos et al, 1996), diffusion into spatially remote areas such as soil macro and micro pores (Ball and Roberts, 1991b; Beck et al, 1995, Burgos et al. 1996; Pignatello and Xing, 1996) and the entrapment within soil organic matter (Brusseau et al, 1991; Fchen et al; Fu et al, 1994). Neutral organic compounds can interact with the soil through a number of attractive forces, such as, dipole-dipole, dipole-induced dipole and hydrogen bonding (Pignatello and Xing, 1996).
Observation indicates that compound sorption to soil exhibits a biphasic behaviour i.e. following an initial rapid phase of sorption there is a subsequent slower but more prolonged period of sorption (Jones et al, 1996; Pignatello and Xing, 1996). This biphasic behaviour has also been observed in thermal desorption studies (Fu et al, 1994), interestingly sorption/desorption processes have a distinct hysterics, where more compound is sorbed than can subsequently be desorbed (Pignatello, 1991: Fu et al, 1994).
Intra-particle diffusion of compounds into macro- and micro-pores may impede biodegradation on the grounds that pores are of a size small enough to exclude micro-organisms (Chung et al, 1993). Exclusion of micro-organisms on the grounds of size is also postulated to occur where compounds becomes entrapped within large humic macromolecules (Fu et al, 1994). It has been noted that where biodegradation has stopped in the case of aged materials, pulverisation (using a ball mill) of the soil resulted in continued biodegradation (Steinberg et al, 1987). This supports the hypothesis that compounds become trapped within soil micropores as aging proceeds. Investigation (Wu and Gschwend, 1986) into the influence of particle size on the rate of sorption/entrapment, revealed much greater rates of uptake for small particles when compared to large ones.
It is evident that the fate and behaviour of organic compounds within the soil environment is dependent on a complex array of processes. Processes which ultimately govern bioavailability, and thereby dictate the feasibility of bioremediation strategies. At one extreme, where compounds are completely available remediation by a biotechnology should prove favourable. At the other extreme where compounds are recalcitrant in nature, such a strategy may fail,
There is a need for a test for the analysis of soil contaminated with persistent organic pollutants to determine whether organic compounds are bioavailable and thereby whether or not a bioremediation strategy will be capable of effecting a sufficient reduction (e.g. to meet legislative requirements) of the amount of pollutants in the soil.
EP-A-0 613 735 discloses a method for the extraction of organic pollutants from contaminated soils. The method involves treatment of the soil with an aqueous solution of a cyclodextrin or derivative thereof. It is stated in this prior specification that cyclodextrins (or their derivatives) enhance the desorption of contaminants from the soil and that this activity can be utilised for the enhancement or the rate of bioremediation of soils contaminated with organic pollutants. As such, the prior specification proposes that the bioremediation of soils contaminated with organic pollutants may be enhanced by treatment of the soil with a cyclodextrin (or derivative thereof) to increase the bioavailability of contaminants to micro-organisms which are capable of degrading the contaminants. However, we have discovered (and this forms the basis of the present invention) that the amount of persistent organic pollutant which a cyclodextrin (or derivative) is able to extract from a soil sample is representative of the amount of the pollutant which is bioavailable and which may therefore be removed by a bioremediation strategy.
On this basis, the present invention provides a test for determining the bioavailable fraction of an organic pollutant present in soil comprising determining the fraction of the organic pollutant present in the soil which may be extracted by a cyclodextrin or derivative thereof.
The present invention is thus to be distinguished from the disclosure in EP-A-0 613 735 in a fundamental way. In the prior specification, the bioremediation strategy is effected by treating the soil inter alia with a cyclodextrin purportedly to increase the bioavailability of the organic pollutant. In contrast, the present invention provides not a bioremediation procedure per se but rather an analysis procedure in which an extraction (of a soil containing persistent organic pollutants) is effected using a cyclodextrin (or derivative thereof) to determine that fraction of the total pollutant which is bioavailable. To a first approximation, the fraction so determined enables a simple calculation to be performed to determine the level of pollutant which would remain in the soil after the bioremediation treatment. Thus it is possible to determine whether the soil is suitable for treatment by bioremediation e.g. to ensure that the remaining pollutant is below legislative maxima.
A preferred test procedure in accordance with the invention comprises the steps of
(a) analysing a first sample of the soil to determine the total amount (or representation thereof) of the organic pollutant which it is desired to remove by a bioremediation strategy,
(b) extracting a sample of the soil with a cyclodextrin (or derivative the

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