Lab Science News

By Elisabeth Lutanie, Ph.D.

Cadmium is a transitional metal that can have harmful cumulative effects on the human body. This article explains what cadmium is, where it comes from, how people get exposed to it, and how laboratories can test for it.

What is Cadmium?

Cadmium (Cd, atomic number 48) is a silver- or bluish-white metal in the group 12 of the periodic table. It is usually found with an oxidation state of +2 and combined with other elements such as oxygen (cadmium oxide), chlorine (cadmium chloride), or sulfur (cadmium sulfate, cadmium sulfide). It is also a cumulative poison associated with an array of syndromes such as renal dysfunction, reproductive toxicity, and bone defects. It is classified as a human carcinogen (Group 1) by the International Agency for Research on Cancer [1], and as a probable human carcinogen (Group B1) by the Environmental Protection Agency (EPA).  

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by Alyson Fortune, Air Quality Scientist; Michael Tuday, Director of R&D; Nicole Pannone, Air Service Specialist

For the past four years, the U.S. Consumer Product Safety Commission (CPSC) has been receiving complaints from homeowners regarding corrosion and odors in their homes linked to imported drywall. The problem drywall, which was installed in homes between 2004 and 2007 and is commonly referred to as “Chinese drywall,” has resulted in more than 2,500 complaints to the CPSC. The complaints originated from homeowners primarily in the southeastern part of the United States, but have since been reported throughout the country.

Homeowners have linked their Chinese drywall to corrosion in their air conditioner coils, corrosion in copper wiring, and emission of foul odors. The odors have been described as smelling like rotten eggs, burnt matches, and other sulfurous smells.

Columbia Analytical has been studying this issue and testing both foreign and domestic drywall samples since February 2008. Laboratory tests have been developed to aid in the identification of defective drywall products. These tests may be used to verify visual home inspections and determine if corrosion effects are from drywall and not from other household items, such as carpets, cleaners, paints, or personal care products.

This article presents a chronology of how Columbia Analytical established their test methods for determining problem drywall and how each of the issues that arose was resolved with a laboratory solution.

See Chinese drywall lab tests and results…

1,4-Dioxane (dioxane) is a chemical of concern for its potential health effects as a carcinogen and irritant. It is commonly found in personal care products such as detergents, shampoos, body lotions, and cosmetics, and is widely used as an industrial solvent and stabilizer in manufacturing processes (e.g., electronics, metal finishing, fabric cleaning, pharmaceuticals, herbicides, pesticides, antifreeze, paper, etc.). Currently, there are no established limits on the amount of dioxane in personal care products nor is it specifically regulated in manufacturing wastewater streams that may impact the surrounding environment. Manufacturers of personal care products should conduct laboratory analysis to determine the levels of dioxane in their products, and manufacturers using dioxane in their processes should analyze their waste streams for possible dioxane content.

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Ultra-trace speciation of arsenic and other metals is performed using a variety of techniques tailored to the specific combination of species, matrix, and detection limits required. Currently, two analytical systems are applied: Ion Chromatography-Inductively Coupled Mass Spectrometry (IC-ICP-MS) and Hydride Generation-Cryogenic Gas Chromatography-Flame Atomic Absorption Spectrometry (HG-CGC-AAS). Each of these techniques has particular strengths that can be exploited depending upon the scientific question being asked. These techniques are combined with specific extraction techniques in order to maximize speciation integrity and data quality.

Ion Chromatography-Inductively Coupled Mass Spectrometry. IC-ICP-MS is a more generalized analytical technique allowing, through optimization of the ion chromatography parameters, the separation of a wide range of inorganic and organic arsenic species in aqueous, geological, and biological media. This technique allows quantification of As(III), As(V), CH₃As²⁺, (CH₃)₂As⁺ (cacodyllic acid), as well as the major forms of arsenic in aquatic organisms: arsenobetaine and arsenocholine at levels less than 0.2 µg/L (ppb) in aqueous solution. After applying gentle, ultra-clean extraction techniques (typically mixtures of aqueous phosphate buffers and methanol) to sediments, soils, or biota, detection limits below 2 ng/g in most solids may be obtained and even lower in biological fluids. Many other arsenic compounds are accessible to analysis by this technique, with the limitation generally being the difficulty of obtaining standards and/or the chemical stability of the compounds. Currently, optimization of this technique has begun for several arsenic compounds of interest to the environmental and food sciences community, including the poultry additives 4-aminobenzene arsenic acid (Roxarsone™) and 4-hydroxy 3-nitrobenzene arsenic acid (para-arsenillic acid), and a natural arsenic metabolic intermediate, tetramethyl arsonium. Additional species, including natural inorganic arsenosulfur compounds and arsenosugars, are also analytes quantifiable by this technique.

Hydride Generation-Cryogenic Gas Chromatography-Atomic Absorption Spectrometry. When lower detection limits are required, HG-CGC-AAS is the method of choice, as sample volumes of up to 100 mL can be concentrated prior to analysis, and high levels of dissolved salts are no problem. Although limited to those species that are inherently volatile or form volatile hydrides, detection limits of <2 ng/L (ppt) are achievable for As(III), total inorganic arsenic (TIAs), CH₃As²⁺, (CH₃)₂As⁺, and (CH₃)₃As (trimethyl arsine, which is difficult to separate at all using IC-ICP-MS). This method is likely most applicable to the low-level quantification of the war gas, Lewisite (2-chloro-ethynl dichloro arsine), which is also inherently volatile at room temperature. Although As(V) is not directly measured using HG-CGC-AAS, it is unambiguously determined as the difference between TIAs and As(III). Thus, it can generally be well quantified in samples where the As(V):As(III) ratio is 0.1 or higher. - Detection limits down to 0.4 ng/g (ppb) are quantifiable in biological and geological solids. In addition, through the use of ultra-clean UV photo-oxidation, you can use this method to determine total arsenic in solution at levels 1-2 orders of magnitude lower than can be obtained using ICP-MS, and with very few interferences.

Speciation of Geological Solids. A variety of sequential selective extraction (SSE) techniques are routinely applied to sediments, soils, and air particulate matter to help further the available speciation information. Comparison of field samples to an array of pure arsenic minerals suspended in kaolin, SSE combined with the speciation methods described above can provide additional insights into solid phase speciation and mineralogy of As in samples such as mine tailings and fly ash. Through a number of collaborative analytical research laboratories throughout the world, more specific solid phase arsenic speciation is available using synchrotron techniques such as EXAFS and XANES, as well as electron microprobe spectrometry (EMPS).

Sampling and Preservation for Arsenic Speciation. As with all trace metals speciation problems, the accurate assessment of arsenic speciation is critically dependant upon the use of the appropriate sampling and preservation procedures. In general, it is important to avoid the use of glass containers (unless inherently volatile species such as (CH₃)₃Hg are being sought), minimize or eliminate contact of the sample with oxygen and other oxidizers, and analyze the sample or preserve it using low-temperature freezing as soon as possible after sample collection. In general, soil and biota samples should be placed in a to-fit trace-clean plastic container and be frozen until analysis. Aqueous samples are best if they are quick frozen in liquid nitrogen or dry-ice plus methanol in appropriate-sized trace-metal clean polyethylene containers provided by our laboratory, and then stored at below -80 ^oC until thawed for analysis. Otherwise, it is best to send most water samples by overnight delivery, unpreserved in completely filled trace-clean plastic containers. Never use containers that have been cleaned with HNO₃ or BrCl, or preserve samples with these reagents. Oxic aqueous samples (surface waters) may be preserved for As(III), As(V), CH₃As²⁺ and (CH₃)₂As⁺ using 0.2% chlorine-free HCl (pre-purged with inert gas) if they will be analyzed using HG-CGC-AAS. Samples of sediment, sediment pore water, groundwater, and/or anoxic water samples have very specific sampling and preservation requirements that should be discussed prior to attempting. It is often best for speciation data quality for your laboratory to provide sampling equipment and personnel for these specialized procedures.

What is RoHS/WEEE?

In 2003 legislation was introduced in the European Union (EU) to promote the collection, treatment, recycling, and recovery of waste from electrical and electronic equipment. This legislation is known as the Waste Electrical and Electronic Equipment (WEEE) act and is formally dictated by directive 2002/96/EC of the European Parliament. A complimentary directive, the Restriction of Hazardous Substances (RoHS), was also introduced in 2003 given by 2002/95/EC of the European Parliament. Beginning July 1, 2006, RoHS legislation restricts the amounts of lead, cadmium, mercury, chromium (VI), Polybrominated Diphenylethers (PBDEs), and Polybrominated Biphenyls (PBBs) in electronic and electrical equipment. These chemicals are known to present a risk to human health and the environment. Thus, restrictions are in place that limit the concentration of these constituents in electrical and electronic products and/or components.

Analytical Chemistry - PBDEs & PBBs

Traditional approaches to the analysis of PBBs and PBDEs have used high-resolution mass spectrometers. While this technique generally has very low detection limits, it is also very costly. As evidence continues to mount regarding the bioaccumulative and toxic effects of PBBs and PBDEs, the need for a sensitive, rugged, cost-effective methods exists.

In response to this need, Columbia Analytical has developed special analytical procedures for the determination of PBDEs and PBBs based upon EPA method 8270C with Selective Ion Monitoring (SIM). The method has been optimized by the addition of Large Volume Injection (LVI), which dramatically increases the sensitivity of the analytical procedure. The procedure provides adequate sensitivity so detection limits significantly lower than the compliance limits set by the European Union (EU) can be met in samples with as little as 10 mg of material available for testing. The standard target list of PBBs and PBDEs at CAS is based upon the environmentally significant and lipophilic congeners. The target list is derived from the primary components of the major products.

Sample Homogenization

The first challenge to producing valid analytical results for electrical and electronic equipment samples is obtaining a representative aliquot for analysis. Samples can range from relatively simple materials (e.g. graphite, gold wire, silicon, etc.) to more complex examples of multi-component assemblies that can include plastics, metal circuitry, solder, etc.

A number of homogenization techniques are employed at CAS. These include ball mills, shatter box, mortar & pestle, Wiley mill, and manual particle size reduction with snips, clippers, etc. In addition to the standard use of these various techniques, cryogenic techniques can be combined to aid the milling process.

The general type of material(s) dictates the homogenization most appropriate for a particular sample. For example, carbon-filled silica is readily ground to a homogenous powder in a ball mill or shatter box. On the other hand, a metallic component is not amenable to milling. A manual approach is generally required to sufficiently reduce the particle size to allow representative sub-sampling, and to provide adequate surface area for efficient digestion and extraction. Generally speaking, brittle materials are processed through one of the mills or mortar & pestle. In cases where a component is pliable, it might be able to be made brittle for milling by freezing in liquid nitrogen, and then carried through the process accompanied by liquid nitrogen. As mentioned, metallic components present the most difficult challenge to homogenization because of their resistance to becoming brittle.

Once a sample is in a homogenous state, it is ready for extraction.

Extraction – PBDEs and PBBs

The solvent extraction procedure for PBDEs and PBBs is relatively simple. Hexane is the extraction solvent. Since fairly small sample masses are common, micro-extractions are generally required. In some cases, as little as 1-2 mg of sample is available, so the extraction is done in an auto-sampler vial prior to instrumental analysis. In all cases, isotopic labeled surrogates and internal standards are added. Two labeled PBDEs are used as surrogates (i.e. C13-Congeners 47 and 49). The internal standard is C13-Congener 118. The same surrogates and internal standards are used for both PBDE and PBB determinations.

Instrumental Analysis – PBDEs and PBBs

Although the level of concern for PBDEs and PBBs is relatively high (i.e. as high as 0.1%), sensitive instrumental techniques are required to compensate for small sample masses often encountered, and to provide adequate sensitivity to get at least ten times lower than the action level. The buffer between the reported detection limit and the action level is important so false positives or negatives can be avoided. From an analytical chemistry standpoint, values reported near the detection limit are subject to considerable variability. Thus, CAS has designed an analytical approach that assures a high level of accuracy and precision at the action level.

The Gas Chromatography-Mass Spectrometry (GC-MS) procedures employed at CAS include Selective Ion Monitoring (SIM) and Large Volume Injection (LVI). The SIM mode allows dwelling on a particular ion so additional signal can be accumulated. The LVI allows a larger volume of sample extract to be delivered to the GC column.

Together, the two techniques improve sensitivity significantly. Selectivity comes from the use of the MS.

For PBDEs, the entire range of bromine substitution is covered by the calibration curve. Although the number of congeners that were historically produced is limited (i.e. less than the 209 theoretically possible congeners), the calibration and identification scheme employed at CAS allows detection of any PBDEs present in the sample. The detection limit reported is calculated directly from the concentration of the lowest standard in the calibration curve. Note that a theoretical detection limit is also determined via precision measurements at the low end of the curve. These values are significantly lower than the limit derived from the low calibration point and serve as validation of the sensitivity of the procedure.

The analysis for PBBs is a bit more complex due to limited availability of PBB congeners. Currently, only the di- through hexa- and the deca- are commercially available for use as calibration standards. (Note: CAS is currently having octa- synthesized). For detections of PBBs with those levels of substitution, fully quantitative results are possible. To provide identification and semi-quantitative information about hepta- and octa- substituted PBBs, commercial fire retardant mixes are analyzed. The commercial mixes have octa- present, as well as small amounts of hepta- and nona-. Semi-quantitative results for those congeners are derived from the response factor for hexa- substituted PBBs.

Analytical Chemistry

Metals Analytical methods are also well developed for measuring metals once in solution. The challenge with electronic and electrical equipment is related to sample preparation, both homogenization and digestion (i.e. getting the target metals in solution ready for instrumental measurement). CAS has numerous homogenization and digestion procedures on line so the appropriate techniques can be applied to each sample on an individual basis. Once satisfactory dissolution of the sample is achieved, the appropriate instrumental technique can be applied. CAS has the capability to select from numerous instrumental techniques to match the correct procedure with a particular sample type. These include Flame Atomic Absorption Spectroscopy (FAAS), Graphite Furnace Atomic Absorption Spectroscopy (GFAAS), Hydride - Atomic Absorption Spectroscopy (Hydride-AAS), Purge & Trap - Cold Vapor Atomic Fluorescence Spectroscopy (P&TCVAFS), Cold Vapor Atomic Absorption Spectroscopy (CVAAS), Inductively Coupled Plasma - Argon Emission Spectroscopy (ICPAES), and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). As with PBBs and PBDEs, this array of options allows for meeting compliance levels in very small electrical component samples (i.e. as small as 1 or 2 mg). The following sections provide more detailed information about the CAS procedure. Note that EPA procedures can be cited for the various techniques employed for digestion and analysis of samples. For some sample types, modification is required to accommodate the material because the scope of the EPA procedures does not cover more advanced applications.

Digestion for Metals

The choice of acid digestions for metals is dictated by the sample type. For non-metallic samples, total dissolution is generally not achieved. This is the result for many samples consisting of materials relatively inert to nitric and hydrochloric acids, or aqua regia (combination of the two). These materials include most plastics, silicon, and carbon based samples. However, by achieving a reasonably fine particle size on these samples, a significant amount of surface area is exposed. Hot, concentrated acids then provide an aggressive leach of the material so the results generated meet the purpose of the regulation. Of particular importance is that the inert materials generally are not the components that would be expected to potentially contain Lead, Cadmium, Mercury, and Hexavalent Chromium.

Samples that contain metallic components or are themselves a metallic material can usually be completely dissolved. Silver and gold components are sometimes present, which require special treatment to achieve dissolution (e.g. dilute nitric for silver; aqua regia for gold). Other metallic components (e.g. solder, micro circuitry, etc.) are readily attacked using aqua regia digestions. For most samples, an aqua regia digestion performed under elevated temperature and pressure in a sealed Teflon bomb is appropriate.

If the sample is digested using the closed vessel approach, Mercury is included through that point. A portion of the digestate is then split and sent for separate handling and further digestion prior to instrumental analysis for Mercury. The other portion of the digestate is ready for Lead, Cadmium, and Total Chromium analysis using the appropriate instrumental approach.

Note: The standard approach at CAS is to analyze for Total Chromium first. If the Total Chromium concentration is below the action limit, then no further determination is necessary (i.e. Hexavalent Chromium cannot be greater than Total Chromium). If Total Chromium is detected near the action limit or above it, then a re-analysis of the sample is performed using an alkaline digestion followed by a colorimetric determination for Hexavalent Chromium.

Instrumental Analysis – Metals

Once the sample dissolution is complete, the final phase of the analysis is normally fairly simple, but does require careful evaluation by experienced atomic spectroscopists. CAS has an array of tools available to satisfy virtually any trace metals application.

Mercury – A portion of the digestate from the bomb dissolution is normally split off for Mercury analysis. Since the action limits for Mercury are high compared to many of the ultra-trace applications at CAS, a simple Cold Vapor Atomic Absorption Spectroscopy (CVAAS), determination is generally satisfactory. The digestate is taken through an additional oxidizing process prior to performing the final reduction of mercuric ions to elemental mercury and detection by atomic absorption.

If a lower limit of detection is needed in the original sample than can be accomplished with CVAAS or the sample is so small that a lower solution concentration is needed, then CAS has the option to analyze the sample by Purge and Trap Atomic Fluorescence Spectroscopy (P&T-AFS), which produces results two to three orders of magnitude lower than conventional CVAAS. To date, CAS has not needed to use P&T-AFS for RoHS applications.

Lead, Cadmium, Chromium (Total) – Lead and Cadmium are generally analyzed by Inductively Coupled Plasma/Mass Spectrometry (ICP/MS), which provides sufficient sensitivity for all applications and selectivity for the majority of applications. Care must be taken to monitor sufficient target and non-target isotopes to address potential isobaric interferences. The standard procedure at CAS is to monitor all potential interferences. Corrective action can be as simple as choosing an alternative isotope or performing arithmetic corrections. However, in some cases an alternative procedure is used to confirm ICP/MS results.

Chromium is measured by Inductively Coupled Plasma/Atomic Emission Spectroscopy (ICP/AES) due to uncorrectable interference from the hydrochloric acid present in the digestate. Both of the primary Chromium isotopes generally used for quantitation by ICP/ MS are overlapped with polyatomic ions derived from the chloride (i.e. aqua regia is used for most digestions). Nonetheless, ICP/ AES offers a satisfactory alternative. Depending on the level of Total Chromium present, future testing to speciate it is sometimes necessary.

Hexavalent Chromium – When the Total Chromium approaches or exceeds the action level, speciation is necessary. Since the action level is relatively high compared to many other applications at CAS, a colorimetric procedure can be used. The technique is essentially identical to EPA Methods 3060A (alkaline digestion) and 7196A (colorimetric determination).

Learn more about RoHS/WEEE compliance testing…

Introduction: Historical mining practices in the Coeur d’Alene River Basin (Idaho) have resulted in heavy metal contamination of soil, sediment, surface water, and groundwater. Canyon Creek, located in the upper basin, has elevated levels of dissolved zinc (average concentration ~ 3,000 μg/L), dissolved cadmium (average concentration ~ 22 μg/ L), and total lead (average concentration ~ 174 μg/L). Heavy metal loading near the mouth of Canyon Creek is influenced by surface water/groundwater interactions. Dissolved zinc concentrations in the groundwater have been detected in the 100,000 μg/L range while dissolved cadmium and lead have been detected in the hundreds to thousands μg/L ranges, respectively.

EPA’s consultant, URS Corporation (URS), developed a multi-phase treatability study to obtain quantitative information on a treatment process to effectively remove metals from the water of Canyon Creek. The treatment process incorporated different combinations of pH adjustment, chemical coagulation and coprecipitation, polymer flocculent additions, and additions of ballasted micro-sand to improve sludge settling. The results of the study will be used to help evaluate potential treatment technologies for surface water and/or groundwater at Canyon Creek. These data will also be used to help develop the pilotscale treatability study for Phase II of the study.

URS contracted Columbia Analytical Services, Inc.’s (CAS) Redding Lab to perform an in-depth, bench-scale treatability study. CAS performed the study in accordance with the procedure described in Canyon Creek Treatability Study Plan, Coeur d’Alene Basin, RAC, EPA Region 10, April 2004 and its Appendix A, Laboratory Scope of Work (SOW).

Treatability Study: The study involved performing a seven step process (see Table 1) involving sixteen jar and nineteen settling rate tests. Varying combinations of lime stabilization (adjusting the pH up to 11) with a calcium hydroxide slurry and coagulation / coprecipitation with ferric chloride followed by polymer flocculation (anion, cationic, and nonionic forms) and micro-sand additions (used as a flocculation aid) were used. The jar and settling rate tests were performed using a 6-place paddle stirrer or jar tester.

The bulk surface water feedstock collected for the treatability study was slightly acidic with a pH of 5.0 and low in conductivity (80 umhos/cm) and hardness (20 mg/L as CaCO3). The bulk sample was received in a Teflon lined 55-gallon drum by over-night courier. To help maintain sample stability the bulk sample was stored in a large walk-in cooler at 4°C for the duration of the study. Sub-samples (each approximately 8-L in volume) were taken for each jar or settling test by mixing the contents of the bulk sample using an acid washed, plastic paddle and then filling a 20-L cubitainer with the sample using an allplastic siphon pump. In addition to the treatability study, CAS analyzed 9 surface water and 4 groundwater samples for ICPMS and ICP metals, general chemistry, physical analyses, and neutralization curve analyses to evaluate site characteristics at the time of feedstock water collection.

Over two hundred samples were generated by the treatment study. CAS immediately analyzed the samples for pH, conductivity, turbidity, and zinc by the Zincon colorimetric procedure. The Zincon method was used so CAS and URS could quickly determine which combination of reagents provided the best reduction in zinc in order to quickly select the optimum combination of reagents for the next jar test. Selected samples were also analyzed for cadmium, lead, and zinc by ICPMS, calcium and magnesium by ICP, and a variety of general chemistry and physical measurements. After Step 3, all zinc analyses were performed by ICPMS because the treatment process was reducing the zinc concentration to below the Zincon detection limit of 20 μg/L.

Study Results: Overall the project was very complicated as each jar test required different combinations of lime, ferric chloride, and different types of flocculating agents depending on the results from the previous jar test. Due to the unknown stability of the water matrix CAS personnel worked through the initial weekend. The testing was completed over a period of 14 days. The bulk sample proved to be stable over this period based on daily analyses of dissolved metals concentrations and conventional parameters.

URS and CAS personnel worked closely with daily communications to insure a smooth progression and successful project outcome. Frequent communications between URS and CAS were essential, as minor modifications to the work-plan were required as the study progressed.

The first phase of the Canyon Creek Treatability Study provided quantitative information on the effectiveness of a variety of treatment approaches for removing dissolved metals from surface water collected from the mouth of Canyon Creek. The treatment process, using the optimum combinations of reagents, resulted in significant reduction of metals plus the formation of a sludge that has very good settling rates and ease of filtering (see Table 2).

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Learn more about testing for mines…

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