CONTAMINATION TEST

Abstract: Method for testing petroleum hydrocarbon contamination in which method a sample is mixed with an alkyl halide extraction solvent. Subsequently the solvent extraction phase is separated, and a Friedel-Crafts Lewis acid catalyst is added thereby obtaining a coloured reaction product in the solvent extraction phase, the colour of which being indicative of the petroleum hydrocarbon contamination.

Description: CONTAMINATION TEST The present invention relates to a method for testing aromatic petroleum hydrocarbon contamination in e.g. soil or water. A known method comprises the steps of: a. taking a sample, b^ adding an excess of an alkyl halide extraction solvent which is such that a solvent phase is obtained containing aromatic petroleum hydrocarbons separated from the sample, c. separating the solvent extraction phase from the soil or water, d _ adding a Friedel-Crafts Lewis acid catalyst to obtain as reaction product a coloured powder, and e. measuring the colour of the coloured reaction product. The colour of the coloured reaction product is indicative of the hydrocarbon contamination of the sample of soil or water. Such a method is known from US-A-4, 992, 379. In this method carbon tetrachloride is employed as alkyl halide extraction solvent. As Friedel-Crafts Lewis acid catalyst anhydrous aluminium chloride is added. This results in the formation of a coloured reaction product which remains bound to the solid phase catalyst. The colour is indicative of the petroleum hydrocarbon contamination. Although the above method provides a testing procedure which is quick and easy to use, certain shortcomings remain. Firstly, identification and quantification are not always straightforward. The identification and quantification consist of comparing the above-mentioned colours with the photographs of standards. Sometimes the colours do not match. Secondly, at the lower and upper end of the concentration range, the photographs of the standard curves lack definition. This makes it extremely difficult to distinguish between the different concentrations by eye with any degree of certainty, which reduces the sensitivity and accuracy of the method. To overcome the above problems, the colours produced in the solid phase in the above test could be measured by using a reflectance spectrophotometer. However, such portable instrument is not commercially available. This makes that the method cannot be used in the field. Thus the usefulness of the test is severely limited. In the testing of samples of soil, it is a further problem that water contained in the soil reduces the efficiency of the solvent extraction leading to an underestimate of contamination levels. It is considered yet a further problem that organic matter other than petroleum hydrocarbons contained in the soil sample can result in overestimation of contamination levels. Thus it is a main object of the present invention to provide a testing method allowing accurate qualification and quantification of aromatic hydrocarbon contaminants present in soil or water. It is a further object of the present invention to arrive at a method adapted both for easy use and for accurately testing samples in the field. Therefore in accordance with the present invention the method as mentioned above is characterized by adding an alkyl halide extraction solvent which is such that after the separating step and the Friedel-Crafts Lewis acid catalyst addition step results in the formation of a coloured reaction product in the solvent extraction phase. This makes it easier to qualify and quantify qualifying and quantifying of the contamination. In a preferred embodiment of the present invention the liquid alkyl halide extraction solvent substantially consists of dichloromethane. When dichloromethane is used, the coloured reaction product to be measured is formed in the liquid phase. It- can be quantified by a portable spectrophotometer which is easy to use at contaminated sites resulting in accurately measured contamination levels. It is further preferred to add a drying agent to a sample, prior to addition of the solvent. The drying agent can be anhydrous magnesium sulphate. Preferably, it is anhydrous sodium sulphate. The drying agent removes water, e.g. from the soil sample. This improves the extraction efficiency. Certain types of polar organic matter can interfere with the test. Such organic matter will most often be found in soil samples. To remove this matter, a polar organic matter adsorbent can be added to the solvent extraction phase. Such adsorbent is silica gel. Preferably aluminium oxide is employed for that purpose. Thus possible erroneous influences on the final contamination levels are avoided in an advantageous way. If water samples are tested, it can be advantageous to add a salting out agent before adding the extraction solvent. In an advantageous way said agent improves the efficiency of the • extraction by forcing the petroleum hydrocarbons out of the water phase into the solvent phase. Preferably salts, such as sodium chloride are employed as salting out agent. A preferred Friedel-Crafts Lewis acid catalyst is anhydrous aluminium trichloride. The present invention further provides a tool kit for testing petroleum hydrocarbon contamination in soil or water, kit comprising at least: - a sample container, a measured amount of an alkyl halide extraction solvent and a Friedel-Crafts Lewis acid catalyst, optionally, a graduated solvent extraction phase container, and a portable spectrophotometer. In a further embodiment of the tool kit, measured amounts of a salting out agent, a dehydrating agent, and a polar organic matter adsorbant are comprised. In particular as spectrophotometer, a colorimeter can be used. The present method can be used for testing any kind of aqueous waste streams, ground-water, surface-water, and effluent streams containing contamination of petroleum hydrocarbons. The invention will be illustrated by the following example. EXAMPLE In order to obtain accurate petroleum hydrocarbon contamination levels the following procedure has been applied. 1. Weigh 5 g soil into a 50 ml screw-top glass container that can be sealed with a cap. 2. Mix the soil with approximately 5 g anhydrous sodium sulphate until the resulting mixture is free-flowing. 3. Add 20 ml dichloromethane (DCM) and shake for about 3 minutes. 4. Allow the soil to settle for 1 minute and remove 5 ml of the clear extraction solvent to a 10 ml screw-top glass test-tube. 5. Add about 0.1 g aluminium oxide and mix well for 1 minute. 6. Add about 0.1 g aluminium chloride and shake periodically for about 10 minutes. 7. Allow the aluminium salts to settle to the bottom of the tube before placing it into the sample holder of the spectrophotometer means and reading the absorbance of the yellow/brown colour at 420 nm against a blank of DCM plus aluminium salts. The colour is stable for at least 24 hours. 8. Convert the absorbance to concentration in the extraction solvent using the appropriate standard curve. 9. Convert the concentration in the extraction solvent to the concentration in the original soil sample. The amounts of reagents as mentioned above are not critical. However, the reagents should be of very high purity (> 99.9%) The above procedure has been applied on a range of soil samples. The results are presented in the table below. TABLE Soil type Contamination Petroleum hydrocarbon concentration (mg/kg soil) lab method (IR) Colorimetric Conventional Sandy Crude oil 43,728 ± 932 44,400 ± 2,828 20,000 - 40,000 Sandy Crude oil 4,618 ± 135 5,320 ± 57 2,000 - 4,000 Clay Diesel 5,404 ± 458 4,812 ± 283 2,000 - 5,000 Clay Fuel oil 1,913 ± 848 2,124 + 147 500 - 1,000 Clay Fuel oil 3,323 + 266 3,158 ± 342 500 - 1,000 I Peaty Unknown 836 ± 24 818 ± 4 500 - 1,000 I method as described in US-A-4, 992, 379. As laboratory method a test in accordance with Environmental petroleum Agency (USA) method EPA 418.1 (1978) was carried out. A Hach DR 2000 (Hach is a trademark) spectrophotometer has been employed in the procedure mentioned above. The limit of detection of the procedure in accordance with the present invention is 100 mg petroleum hydrocarbon contamination/kg (soil) for complex mixtures such as gasoline, diesel, and crude oil, and 10 mg contamination/kg (soil) for monoaromatic hydrocarbons such as benzene, toluene, xylene, and polyaromatic hydrocarbons such as naphthalene. The appropriate standard curve is prepared prior to the series of tests. From the above table it may be clear to those skilled in the art that very accurate data have been obtained by using the method in accordance with the present invention. Further to the above it will be clear to a skilled person that depending on the level of contamination in the sample the solvent extraction phase can be diluted with an appropriate solvent prior to carrying out the catalyst reaction in order to ensure that the absorbance falls within the linear range of the spectrophotometer used. Accordingly calculations of concentration have to be adapted. As to samples of contaminated water, for example ground water, waste water or any kind of contaminated aqueous streams, 1 1 of sample can be extracted with 20 ml of appropriate solvent. In such an experiment the two phases can be separated advantageously in a separating funnel, allowing the lower solvent extraction phase to run into a solvent extraction phase container means preferably containing 5 g of anhydrous sodium sulphate to dry the sample prior to carrying out the colour reaction and subsequent quantification.

Claims: C L A I M S 1. A method for testing petroleum hydrocarbon contamination, the method comprising the following steps: a. taking a sample, b. adding an excess of an alkyl halide extraction solvent which is such that a solvent phase is obtained containing petroleum hydrocarbon, and such that in step cL_ a coloured solvent extraction phase is obtained, c. separating the solvent extraction phase from the soil or water, d. adding a Friedel-Crafts Lewis acid catalyst thereby obtaining a coloured reaction product in the solvent extraction phase, and e. measuring the colour of the coloured reaction product. 2. The method as claimed in claim 1, wherein the alkyl halide extraction solvent is dichloromethane. 3. The method as claimed in claim 1 or 2, wherein the Friedel- Crafts Lewis acid catalyst is anhydrous aluminium trichloride. 4. The method as claimed in claim 1, further comprising the step of adding a dehydrating agent to the sample of soil after the sample has been taken in accordance with step a.. 5. The method as claimed in claim 1 or 4, further comprising the step of adding a polar organic matter adsorbant to the alkyl halide extraction solvent after separation from the soil in accordance with step c.. 6. The method as claimed in claim 1, further comprising the step of adding to the sample of water a salting out agent after the sample has been taken in accordance with step a.. 7. The method as claimed in claim 1, wherein the colour of the coloured reaction product is measured by means of a portable spectrophotometer means. 8. A tool kit for testing petroleum hydrocarbon contamination of soil or water, the kit comprising at least: a sample container, a measured amount of an alkyl halide extraction solvent reagent and a Friedel-Crafts Lewis acid catalyst, optionally, a graduated solvent extraction phase container, and a portable spectrophotometer. 9. The tool kit as claimed in claim 12, further comprising measured amounts of a salting out agent, a dehydration agent, and/or a polar organic matter adsorbant. 10. The tool kit as claimed in claim 8, wherein the portable spectrophotometer is a colorimeter.

Inventors: LADD DEVJI DALUBHAI, LETHBRIDGE GORDON, LINNETT PAUL ERIC, LADD, DEVJI, DALUBHAI, LETHBRIDGE, GORDON, LINNETT, PAUL, ERIC
Applicants: SHELL CANADA LTD, SHELL INT RESEARCH, SHELL CANADA LIMITED, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1995
Main classification: G01N33
IPC codes: G01N33