Soil Contaminant Analysis

Organic contaminants encompass a wide array of compounds determined as harmful or detrimental to human and environmental health. Many of these compounds are human-made chemicals that are used and produced in industrial, manufacturing and agricultural activities. Due to the potentially drastic impact of contamination and high susceptibility of soil to pollution accumulation such as agricultural runoff of pesticides, this environmental matrix is routinely analyzed for the presence of xenobiotic compounds. Exposure to contaminated soil has the potential to directly affect human health through either direct contact or indirect contamination of ground and surface water systems.

Regulatory bodies attempt to streamline the cost of known contaminant compliance monitoring by regulating them as groups with similar health effects, co-occurrence, common analytical methods, and common treatment or control practices. In addition to known contaminants, unknown compounds pose a serious threat to environmental protection and create a growing challenge across the globe.

To analyze soil for the presence of a vast assortment of compound classes and meet regulatory requirements a robust strategy is needed that employs various analytical techniques. Workflows that support sample preparation and analysis for different soil types have to be considered in order to successfully extract, identify and quantitate compounds. Extraction approaches typically include solvent exchange, solid phase extraction (SPE), accelerated solvent extraction (ASE) and/or microwave extraction methods. Chromatographic separations and Mass spectrometry techniques provide the bulk of identification and quantitation data for these compounds in environmental matrices. Common analytical methods for analyzing organic contaminants in soil include GC, HPLC, IC, GC-MS, IC-MS and LC-MS. The Thermo Fisher Scientific environmental analysis portfolio provides tailored systems for all of these routine chromatographic and mass spectrometry techniques with comprehensive workflows that enable laboratories to effectively and efficiently meet today’s organic contaminant regulations and prepare for the evolving needs of tomorrow.

Download application note AN10441 and AN20677

To accurately analyze the pesticides in soil, the pesticides must first be extracted from soil using accelerated solvent extraction (ASE) and applied to gas chromatography-mass spectrometer for targeted or untargeted analysis.

Download flyer SS52180

Instruments and consumables used for organic contaminant analysis:

At least 17 nutrients are essential for plant growth. Some are macronutrients (existing in larger amount), such as nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur, while others are micronutrients, including boron, copper, iron, manganese, and molybdenum, and others. It is critically important to know the quantity of available nutrient in both soil and compost (such as biosolids) so the right kind and amount of fertilizer can be applied. Overuse or lack of nutrients will reduce the plant growth potential, and leads to resource waste and even contamination of the soils. For soil and compost nutrient analysis, multiple routine parameters need to be measured with different technologies.

Soil macronutrient testing

Element analyzers

Macronutrients are necessary to measure for identification of soil quality. They can be quantified by element analyzers using combustion to convert the elements to gaseous form and further separated by gas chromatography.

• Nitrogen—nitrogen in soils is important for the evaluation and calculation of the amount of fertilizer to be added for plant growth. Nitrogen content quantitation is critical for determination of the quality of various types of crops for feeding and processing, as well as for N-cycle and N-fixation monitoring in agricultural and environmental research. The detailed detection method using the argon gas can be found in the application note 42202.
• Total carbon, total organic carbon and CHNS—Due to the heterogeneity of the material used for compost, accurate control of parameters such as nitrogen, total carbon, total organic carbon (TOC) and sulfur content in the recycled waste is a key factor to ensure the high quality fertilizer. The application note 42197 describes the measurement method.
• Sulfur—like carbon and nitrogen, sulfur is also an essential component of living being through uptake and synthesis of several amino acids: cysteine, cystine and methionine. The deficiency of sulfur has a negative influence in the growth of vegetable crops. In addition, the levels of sulfur detected in leaves and pine needles are also an indicator of environmental pollution. For more information on the analysis of sulfur, download the application note 42187.

For additional information, download the cook book.

All of these analyses can be performed by the following instruments:

MAS 200R autosampler → FLASH 2000 NC Soils Analyzer

Nutrient analysis

In addition to element analyzers, discrete analyzers can also be used for potassium and phosphorus analysis. Different from the element analyzers that determine the nutrients by the property of the elements, the discrete analyzers use specific chemical reactions from nutrients and certain chemicals to generate colors that can be detected by discrete analyzers. Besides testing the soil, discrete analyzers are also used for drinking water and wastewater analysis.

View the case study for fertilizer analysis.

Mineral analysis

The growth of plants needs mineral elements. These mineral nutrients are micronutrients as they are required in very small amount (often in the ppm level). The mineral elements are metal elements and often are analyzed by ICP-OES.

The mineral nutrients have to be extracted from the soils before they are analyzed. There are multiple extraction methods, such as DTPA-TEA, HCL solution, Mehlich-1, Mehlich-3, and total digestion (EPA 3050B, 3051A, and 3052 Method). Depending on the requirement, different extraction methods can be used.

Mineral analysis can be performed using the following instruments:

Microwave digestion system (from CEM) → CETAC™ Autosamplers → iCAP™ 7600 ICP-OES Analyzer

In addition to the mineral metal elements, toxic heavy metals in soils, such as arsenic (metalloid), cadmium, lead, and mercury, can also be analyzed using the same technology, or more sensitive cold vapor atomic absorption spectrometer, cold vapor atomic fluorescence spectrometer, or ICP-MS technology. Quantifying these elements is required for biosolids used as fertilizer and the soil screening by the U. S. EPA. It is necessary to keep these toxic metals in really low level to keep the soil and plants away from contaminants and prevent us from eating polluted food.

Multiple technologies have been used for heavy metal analysis based on chromatography, spectroscopy, and electrochemistry.

ICP-OES and ICP-MS

When using ICP-MS for soil sample analysis, it is important to keep in mind the limitation of the ICP-MS for total dissolved solid (TDS). Typical ICP-MS can handle less than 0.2% TDS. However, with argon gas dilution or autodilution techniques, tolerance to high matrix is improved for ICP-MS analysis.

Instruments for ICP-MS analysis of toxic heavy metals:

CETAC™ Autosamplers → iCAP™ Q ICP-MS

Haxavelent chromium (Cr (VI)) is also a toxic species from different industries such as chemical and leather tanning industries. It is regulated in California in drinking water and soil.

The U.S. EPA has approved:

• Ion chromatography analysis of Cr (VI) in Method 218.7 for drinking water
• Ion chromatography analysis of Cr (VI) in ground water and industrial wastewater in SW846 Method 7199
• The EPA SW846 Method 3060A for extraction of Cr (VI) from soil

We also developed ion chromatography method using accelerated solvent extraction (ASE) to prepare the samples and further quantify Cr (VI) by ion chromatography via post-column derivertization. Download the poster note 70729.

Instruments for Cr (VI) determination in soil:

Dionex™ ASE™ 350 Accelerated Solvent Extractor → Dionex™ ICS-5000+ Hybrid HPIC™ System → Dionex™ Chromeleon™ 7.2 Chromatography Data System

X-ray fluorescence (XRF) analyzers

Portable XRF is a powerful tool to detect heavy metal elements in soil. Analyzing up to 25 metals at one time, the XRF analyzers can analyze soil samples on the spot without the need of sample digestion. The EPA SW846 Method 6200 uses XRF for metal analysis in solid waste and soil analysis. However, the method’s low detection limit is usually higher than the regulatory level for most analytes regulated in RCRA (Resource Conservation and Recovery Act). It is used as a confirmatory method for atomic absorption technologies (such as ICP-OES and ICP-MS) in determination of metals. Nevertheless, the instrument is a great tool for on-site screening and quality control applications.

Not only is XRF used for heavy metal analysis, other elements such as S, P, Al, Mg, Si, and U, can also be analyzed.

For more information on XRF in soil applications, visit X-Ray Fluorescence (XRF) page.

Sorbents and post extraction clean-up cartridges can be used to cleanup unwanted interferences. 

• In-cell extractions, using the sorbents of choice, remove interferences and allow for complete automation of extraction and post-extraction cleanup steps. This option reduces overall costs and preparation time, and increases sample throughput.
• Post-extraction clean-up cartridges provide a choice of sorbents to clean-up the extracts while reducing the likelihood of solvent interactions with the sorbents at elevated temperature and pressure.