Manual for Soil Analysis-Monitoring and Assessing Soil Bioremediation Phần 4 doc

98 K.S. Jørgensen et al.

The biodegradation rate can be linear or represent first order decay depen￾dent on, e.g., the contaminant concentration and bioavailability. Field-scale

bioremediation can be classified as either in situ methods, where the treat￾ment takes place without excavating the soil, and ex situ methods, where ex￾cavated soil is treated typically in piles. When monitoring a site undergoing

in situ treatment by drilling for subsurface samples, it is essential to remem￾ber that true replicate samples cannot be obtained and a large variation is to

be expected. When sampling stock piles or biopiles, a combination sample

consisting of subsamples from different places in the piles typically will be

assembled, and parallel combination samples can be made (Jørgensen et al.

2000). When monitoring biodegradation by laboratory microcosms, it is of

great importance that all the sample material representing a certain depth,

treatment, etc., is homogenous. This is best ensured by homogenizing and

sieving a larger batch from the field and by distributing this into separate

parallel bottles or other containers for laboratory incubations. A mesh size

of 8 mm has proven to be a good size for sieving field-moist soil (Laine

and Jørgensen 1997; Salminen et al. 2004). However, the measurement of

contaminant disappearance only shows that the parent compound has been

transformed; it does not reveal whether the degradation is complete to CO2

or CH4 or if other degradation products are produced.

Contamination with petroleum hydrocarbon products is one of the most

frequent types of soil contamination. Refineries, surface and underground

storage tanks, petrol service stations, etc., are the most common sites for

such contamination. Most petroleum products also contain minor amounts

of PAHs. No single method is reliable for the determination of all petroleum

hydrocarbons, and we therefore describe three methods for the determi￾nation of different fractions of hydrocarbons in soil samples.

Volatile hydrocarbons (Sect. 3.2) should be determined at sites where

gasoline and jet fuel are the sources of contamination. The pertinent

method here quantitatively determines these separate compounds: ben￾zene, toluene, ethylbenzene and xylenes (BTEX compounds), naphthalene,

and gasoline additives such as MTBE (methyl tert-butyl ether) and TAME

(tert-amyl methyl ether). This method can also be used to determine halo￾genated volatiles, which may often be found together with fuel products

because such solvents often are used, e.g., for cleaning engines.

Contamination with oil products such as heating oil, diesel or lubricating

oil is best determined using the method (Sect. 3.3) for hydrocarbons in

the range C10 to C40. The result is a sum parameter, which does not give

concentrations of specific compounds. But still the sum of the hundreds of

compounds in this range is very useful for quantifying contamination with

them and for monitoring bioremediation. Based on the chromatogram,

a qualitative estimation of the type of contamination can be obtained.

This C10–40 parameter is often referred to as mineral oil or total petroleum

3 Quantification of Soil Contamination 99

hydrocarbons (TPH), but these terms are somewhat unspecific. Crude oil is

often determined with this method, but it also includes volatiles and PAHs

that should be determined separately with the methods for volatiles and

PAHs, respectively.

Contamination with PAHs is commonly found at gas works and at sites

where coal tar and oil shale are handled. Oil containing heavy fractions

or waste oil may also contain significant amounts of PAHs. The method

described here (Sect. 3.4) allows for a single determination of 16 different

PAH compounds. In the literature the sum of PAHs is often reported, but

the fact that different countries and different laboratories analyze different

number of compounds has made this term very unspecific. Guideline values

for clean-up needs also differ between countries, so it is important to

check which compounds require reports. Since the toxicities of the PAH

compounds differ, there may not be any guideline value set out for all

compounds.

Contamination with heavy metals is difficult to assess because clean

soil itself may contain many heavy metals, depending on the geological

structure. Furthermore, many metals are not necessarily bioavailable in

soil, and for that reason different types of less exhaustive extractions are

being developed to determine the bioavailable fractions. The background

contents of metals in soil are in many countries known and they are taken

into account when guideline values for clean-up are determined. Still today

most guideline values are based on the total or near-total content of metals.

The method described here (Sect. 3.5) reveals the near-total content and is

aiming at determining the anthropogenic contamination.

3.2

Volatile Hydrocarbons

■ Introduction

Objectives. The volatile organic compounds (VOCs) in soils primarily orig￾inate from petroleum products and solvents. The spectra of the VOCs de￾pend on their source. The analysis of benzene, toluene, and ethylbenzene

and xylenes (BTEX) is widely used as an indicator of contamination with

light petroleum products, e.g., petrol and kerosene. Furthermore, the gaso￾line additives MTBE and TAME as well as halogenated volatile compounds

can be analyzed with this method.

Principle. A soil sample is extracted with methanol. A defined volume of the

methanol extract is transferred into water and the water sample is heated

to 80 ◦C in a headspace vial. When equilibrium is established between the

gaseous and liquid phases, an aliquot of the gaseous phase is injected on

100 K.S. Jørgensen et al.

a column of a gas chromatograph and the VOCs are determined with a mass

selective detector.

Theory. VOCs are a group of compounds that have a boiling point from 20

to 220 ◦C and usually they have two to ten C atoms. They are mainly un￾substituted or substituted monoaromatics and short-chain aliphatic com￾pounds that differ in solubility and in toxicity. The individual compounds

are quantitatively determined using this method, as can also be the diaro￾matic compound naphthalene. We do not recommend measuring the sum

of VOCs because such a sum is unspecific and depends on the compounds

included.

The sampling (ISO 10381–1 1994; ISO 10381–2 1994; Owen and Whittle

2003) is a crucial step in the analysis of VOCs. In order to prevent their loss

during preparative steps, field-moist samples are used (ISO 14507 2003).

The sample is added into a pre-weighed glass container containing a known

amount of methanol. To control the quality of the determination, field du￾plicates, a procedural blank, and a control sample are analyzed. The two

main methods of analysis of VOCs are static headspace/gas chromatogra￾phy (e.g., ISO/PRF 22155 in prep.) and purge and trap/gas chromatography

(e.g., ISO 15009 2002). In the analysis of volatile aliphatic and aromatic

hydrocarbons a mass selective detector (MSD) is used. VOCs can also be

detected with a photo ionization detector (PID), a flame ionization detec￾tor (FID), and an electron capture detector (ECD; Owen and Whittle 2003).

The identification of target compounds (ISO/DIS 22892 in prep.) is easy

with a MSD, and a possible matrix effect can be eliminated. The method

described here is that using static headspace/gas chromatography (MSD)

and is based on the proof of a new international standard ISO/PRF 22155

and has earlier been described by Salminen et al. (2004).

■ Equipment

• Usual laboratory glassware, free of interfering compounds

• Shaking machine

• Headspace analyzer and gas chromatograph with a mass selective detec￾tor (MSD)

– Oven temperature program: maintain 35 ◦C for 2 min, then steadily

raise by 14 ◦C/min up to 90 ◦C. Maintain 90 ◦C for 5 min, then raise

by 12 ◦C/min up to 190 ◦C. Maintain 190 ◦C for 1 min, then raise by

40 ◦C/min up to 225 ◦C, and maintain at 225 ◦C for 1 min.

– Carrier gas: helium.

– Gas flow: 10 mL/min.

– Split ratio (gas flow rate through split exit: column flow rate): 5.7:1.