“Chinese Drywall”, also called odorous gypsum wallboard, is an emerging issue in the IAQ community. The material, which has been identified in new and remodeled homes in Florida, Louisiana, Texas, and reported elsewhere, has been determined to emit chemicals that cause characteristic sulfide odors, black discoloration of metal fixtures, electrical components, and domestic water piping, as well as black sulfide corrosion of HVAC components leading to failure. There are also reports of health effects associated with the material. This article explores the history and underlying conditions that caused the problem, assessment strategies for evaluating whether a property has been impacted by the problem, tools for identifying affected materials, and some goals for remediation of the problem.

History

In late 2006, reports of new Florida homes with strange, persistent sulfur odors surfaced. Consultants working for builders and purchasers began performing air sampling to try to quantify the problem, often choosing EPA Method TO-15 for volatiles, as well as other methods for sulfur compounds such as hydrogen sulfide (H2S) and sulfur dioxide (SO2). In most cases, nothing unusual was found, however, in a few instances, slightly elevated levels of carbon disulfide (CS2), and carbonyl sulfide (COS) were found.

At about the same time, consultants working for a major builder, suspecting that the gypsum wallboard used to construct the homes was the culprit, had samples of the material tested for anything unusual. The material was traced to a distributor who had imported the material from a manufacturer in China. It was reported that the material contained elevated amounts of iron disulfide (iron pyrite), and emitted elevated levels of carbon disulfide, hydrogen sulfide, and carbonyl sulfide. Subsequent studies done by others turned up problem wallboard by at least one additional Chinese manufacturer. SO2, mercaptans, thiophenes, and dimethyl sulfide (DMS) have been also reportedly identified, by modified head-space analysis. Increased organic content (as loss of ignition and total organic carbon) and pH of the bulk material have been also reported.

In 2007, and throughout 2008, another seemingly unrelated symptom began to occur in the same population of homes in Florida – rapid failure of air-conditioning evaporator coils with loss of refrigerant, often within months of installation. Analysis of the coils turned up severe pitting sulfide corrosion of the copper tubing comprising the coils, visible as a black, sooty, pitted appearance, as opposed to a normal smooth, brown or red appearance. In several cases, replacement coils underwent the same corrosion and failure process, again, within months.

Economic, Demographic, Weather, and Climate Factors

Traditionally the weight and bulk of wallboard, and the shipping costs entailed have hampered the economics of importation of the material. Beginning in about 1998, and increasing in 2001 – 2007, a convergence of factors caused a historic construction boom in Florida. According  to Florida Tax Watch, over a million new homes were started between 2001 and 2007, echoing a trend across the US. Loosened monetary policy and interest-rate cutting by the Federal Reserve, particularly after the terrorist attacks of September 11th, 2001, led to unprecedented levels of housing construction nationwide.

For demographic and economic reasons Florida was particularly affected. The Florida  Office of Economic and Demographic Research indicated a population increase of over 2 million during that time. Severe storms across the entire Gulf States region in 2004 and especially Hurricanes Katrina, Rita, and Wilma in 2005 drove home reconstruction and rebuilding markets higher, increasing demand pressure on  supplies of building materials, including gypsum wallboard. Over 300,000 homes were destroyed or significantly damaged. This resulted in increased imports of drywall to the region, especially from China. Most of the material appears to have been distributed through wholesale rather than retail channels. The coastal regions of the Gulf States (Florida, Louisiana, Mississippi, Alabama, and Texas) also have higher than average temperature and humidity levels, which contribute to the phenomenon.

Assessment - Distinguishing Characteristics

Traditional drywall is made of a core of gypsum pressed between two thick layers of paper. Therefore, the main crystalline components in the drywall are gypsum (CaSO4.2H2O) and plaster (CaSO4.1/2H2O). The raw material (gypsum) is also mixed with various additives such as paper, fibrous glass (both added to acquire mechanical strength), some plasticizers (to improve workability), vermiculite, perlite (to improve the fi re resistance), and various chemicals for mildew resistance. The source for gypsum is usually mining or flue gas desulfurization process, where gypsum is obtained as by-product.

Some of the odorous drywall material appears visually dark gray compared to domestically- produced wallboard. Other affected material might be tan or gray in color, compared to white or light grey for domestically-produced wallboard. Mild odors are sometimes noted on samples, but they might be subtle or even absent in desiccated samples. However, samples conditioned with humidity and temperatures do have a pronounced carbonyl sulfide odor like burnt fi reworks.

Several theories have been advanced as to why the defective product possesses its unique characteristics. Initial reports from one manufacturer seemed to suggest that the problem was iron pyrite contamination of natural mined gypsum product. Analysis of the material would seem to contradict this, since the material has elevated levels of magnesium that would seem to indicate that the gypsum was derived from a flue gas desulfurization process using calcite. Others have suggested that the material contains fl y ash from coal combustion.

Building Assessment

Assessing buildings for the presence of odorous drywall can be a challenging task. Buildings built or modified prior to 2004 are unlikely to exhibit the symptoms; however the date of construction in a given dwelling isn’t always easily determined. According to the Florida Department of Health, buildings possessing three or more of the following conditions regardless of apparent age;

• Presence of sulfur-like or other unusual odors
• Confirmed presence of Chinese manufactured drywall in the home
• Observed copper corrosion, indicated by black, sooty coating of un-insulated copper pipe leading to the air handling unit present in the garage or mechanical closet of home
• Documented failure of air conditioner evaporator coil (located inside the air handling unit)
• Confirmation by an outside expert or professional for the presence of premature copper corrosion on un-insulated copper wires and/or air conditioner evaporator coils (inside the air handling unit)

Buildings that do not meet two or more of the above criteria likely do not contain signifi - cant amounts of the odorous drywall. Buildings meeting two or more criteria are candidates for bulk sampling to confi rm and verify the presence and extent of the suspect material.

Identification - Analytical Methods

The selection of the most appropriate analysis approach to determine the source or the sources of the sulfur-based odor in the sub-par drywall is still controversial. The elemental analysis of the bulk drywall to determine the concentration of impurities (such as iron, strontium, magnesium, phosphorus, chlorine, etc, reported as elements, and not as compounds that might contain these elements) is one approach. The analysis can be performed using methods available to determine the overall elemental composition of the material in this type of matrix (such as XRF, SEM/EDX, XRD).

X-ray Fluorescence (XRF) analysis of various samples of drywall performed in our laboratory revealed anomalies with respect to the presence of iron (Fe), strontium (Sr), magnesium (Mg), and sometimes phosphorus (P) in the odorous drywall when compared to domestically- produced drywall (see chart on page 24). The exact identity of the compounds formed by these elements is still under investigation.

Scanning Electron Microscopy with Energy dispersive X-ray spectroscopy (SEM/EDX) analysis of selected impurities extracted from the odorous drywall revealed the presence of sulfur in association with Fe and Sr, indicating the presence of possible pyrite (FeS2) and strontium sulfide (SrS). These compounds could decompose in hot and humid conditions. SrS, for example, slowly releases H2S in moist air. It is speculated that the presence of these compounds in low concentrations as impurities is related to mined gypsum. No evidence of fl y ash as determined by optical microscopy was determined in the samples analyzed in our laboratory.

X-ray Diffraction (XRD) can be used to determine the crystalline components in the sample. A typical result for this analysis would show the presence of gypsum (CaSO4.2H2O) as the main component, along with low concentrations of anhydrite, semi-hydrite, and quartz. It is important to mention that XRD method in bulk and this type of matrix has a detection limit of 1-2%. Therefore, crystalline particles that are in concentrations below these limits cannot be detected by this method (such as pyrite and SrS allegedly present).

Off-Gas Sampling by GC/MS. As mentioned earlier, indoor air sampling by EPA method TO- 15 or ASTM D-5504 have not been very successful, with no more than 10% of indoor air samples taken in affected spaces showing anything unusual. This may be due in part to low concentrations in air, moisture conditions, and inappropriate selection of collection canisters. Therefore, modified methods employing GC/MS analysis of the volatile and semi-volatile organic compounds, either via environmental chamber approach, head space, or BNA extraction are used.

Headspace/chamber analysis of humidified samples of wallboard has been consistently successful in identifying the odorous material. Samples of the gases collected from wallboard samples in the laboratory via environmental chamber approach consistently showed elevated levels of carbon disulfide and carbonyl sulfide. It has been noted that the humidity of the sample greatly influenced the off-gassing event by increasing the concentrations of the sulfurcontaining gaseous compounds 2-3 fold. Other reports showed increased off-gassing with increasing temperature.

Corrosion simulation. A common problem related to the odorous drywall is the corrosion of un-insulated copper piping or wires, indicated by black powdery deposits on the surface of the metal. This phenomenon is commonly known as black copper corrosion. The corrosion usually develops on surfaces such as air conditioning evaporator coils, exposed copper of wiring on the electrical panel inside air handling units. (The corrosion could also show as darkening on the edges of mirrors, corrosion of light fixtures, sink faucets, and door or cabinet hinges).

The propensity of the drywall to corrode copper could be determined in laboratory experiments by exposing fresh copper coupons or piping to the eventual gases emanated from the drywall. For achieving accelerated exposure conditions, the drywall could be stripped from the protective paper layers, the coupons could be placed in direct contact with the exposed drywall material, and the temperature and humidity conditions could be selected to mimic hot and humid climate.

Simulated corrosion experiments performed in our laboratory using drywall that was tested positive for sulfur-containing gases showed variable time-frames for developing the black copper corrosion. In accelerated conditions, the advanced corrosion in the form of black film of copper sulfide developed on the surface of the coupon was noted as fast as 13 days of exposure at 95% humidity and 98°F. In gentler exposure conditions (protective paper in place, 85% humidity, 98°F), the corrosion was less advanced and it developed in 6-8 weeks of exposure.

Microbiological approach. Sulfur odors may also be produced when certain aerobic and anaerobic bacteria utilize certain molecules for growth. Therefore, endotoxin analysis for gram negative bacterial contamination and sulfur reducing and iron related bacterial tests may be recommended.

Various other methods such as Fourier Transformed Infrared Spectrometry (FTIR) or Infrared Imaging have been advertised as being successfully used to identify the “Chinese drywall” by analysis of the bulk material. However, considering the general usage of these methods and the principle of operation, these methods could be used, at most, as screening procedures.

Potential Health Impacts

Although materials emitted from the odorous drywall are capable of causing serious damage to building and furnishing materials, the impact of these emissions on human health is unclear. Reasons that health-impact data is lacking include low and variable air concentrations, and limitations of available sampling and analytical techniques. Symptoms (including eye irritation, respiratory irritation, headache, and nosebleeds) have been reported by occupants of some, but not all affected spaces. Toxicology reports available from the Florida DOH and other sources suggest that the sulfur-containing gases are present at levels that do not pose health risk. But based on the previously-noted infrequent detection of limited amounts of air contaminants, it is  difficult to say with any certainty what short- or long-term health impacts might proceed from exposure to the affected material.

Agencies and Guidelines:

NIOSH: Formed by the DHHS as a branch of the CDC by the OSHA Act, NIOSH develops and recommends criteria for preventing disease and injury in the workplace. Recommended Exposure Limits (RELs) are an example of such criteria, based on reviews of scientific literature. NIOSH communicates the information to OSHA for use in rulemaking. The NIOSH REL for carbon disulfide is 1 ppm. The NIOSHREL for hydrogen sulfide is a ceiling limit of 10 ppm. NIOSH has no REL for carbonyl sulfide.

ATSDR: Another branch of the CDC, the Agency for Toxic Substance and Disease Registry concentrates on evaluating evidence for nonoccupational (i.e., residential) exposures to toxic chemicals and setting recommendations called Minimal Risk Levels (MRLs.) The current MRL for carbon disulfide is 0.3 ppm (300 ppb) The current MRL for hydrogen sulfide is 0.07 ppm (70 ppb). There is no MRL for carbonyl sulfide.

USEPA: The United States Environmental Protection Agency (USEPA) publishes Risk- Based Concentrations (RBCs) based on conservative risk estimates, which are in turn based on both experimental and epidemiological studies of exposure to hazardous chemicals. The RBC for carbon disulfide is 0.234 ppm (234 ppb). The current RBC for hydrogen sulfi de is 0.015 ppm (1.5 ppb). There is no RBC for carbonyl sulfi de.

Criteria For Remediation

Once the problem has been adequately assessed, and the odorous materials identified, the property will need to be remediated. The goal of remediation is a permanent solution that protects both occupant health and building system integrity. Since the source of the problem is known, and able to be observed, source removal suggests itself as a possibility, though it is likely to be very expensive and difficult to undertake, though verification is somewhat easier. Affected HVAC and electrical components will need to be decontaminated or replaced; some verification techniques are available for this. Other building elements, such as studs, other structural members, masonry, and sheathing, along with possibly being damaged by emissions from the wallboard, may potentially serve as secondary emission sources. Tools for assessing this are relatively lacking and will have to be developed.

The odorous gypsum wallboard or “Chinese drywall” problem is a definable, solvable problem. The pertinent geography and time period for the problem are well-understood. Criteria for assessing and verifying the presence of the material are well-defined. Positive identification of the material is accomplished by XRF /XRD, GC/MS, and copper corrosivity tests. Remediation criteria are clear, and can be verifi ed. The key to solving the problem is a systematic, scientific, evidence-based approach that is mindful of economics, and protective of human and building health.

Vincent M. Daliessio Jr.,CIH serves as Industrial Hygiene Project Manager for EMSL Analytical in Westmont, NJ. He has spent most of the last 20 years anticipating, recognizing, evaluating, and controlling hazards in indoor and ambient environments. One of his current projects is developing tools for evaluation of the Chinese Drywall problem. He can be reached by e-mail at This e-mail address is being protected from spambots. You need JavaScript enabled to view it , or by phone at 1-800-220-3675, extension 1240. Eugenia Mirica, Ph.D., is the Project/Client Services Laboratory Manager of the Materials Science Division and Senior Materials Scientist at EMSL Analytical, Inc., Westmont, NJ. She joined EMSL Analytical in 2002 where she has been working on analyses for materials identification, morphological and chemical characterization of materials, product comparison, contamination control, and forensic analysis. She can be reached by email at emirica@emsl. com or by phone at 1-800-220-3675, ext. 1247.