Heavy Metals, their Salts, and other Compounds A Quick Reference Guide from AIC and the Health & Safety Committee A Special Insert By Cheryl Podsiki Figure 1. The 35 shaded elements in this periodic table are those regulated by OSHA under the classification of Heavy Metals [1, 2]. Introduction trace element and beryllium, a light is an essential trace element [6] and its but very toxic metal [4]. All metals are compounds, including soluble chro- The term heavy metal is a loosely characterized by their excellent abil- mium salts, are considered to be of used term generally accepted to mean ity to conduct heat and electricity (the low toxicity and are thought to present dense metals of relatively high atomic metalloids being semi-conductors), and few industrial hazards [22]. Hexavalent mass, with a specific gravity of 4 or are malleable, ductile, hard, and shiny, chromium, Cr (VI), however, is highly above. Although there are several the exception being mercury which is toxic [6] and its compounds, includ- other definitions of the term there is liquid at room temperature. ing chromic acid and chromates, are no specific set of elements that would One of the most significant fac- potential carcinogens [22]. imply any common set of properties tors about metals is their residual Posted on the AIC website, the such as high toxicity or high atomic persistence over time. Metallic com- “Chart of Heavy Metals, their Salts, weight [3]. The heavy metals group pounds such as oxides, sulfides, chlo- and other Compounds” provides a includes transition metals, some met- rides, carbonates, nitrates, and other quick reference to the 35 elements alloids (elements that exhibit both salts are formed when positively and some of their compounds classi- metal and non-metal properties), some charged metals called cations react with fied and regulated by OSHA as heavy lanthanides and actinides, and often negatively charged elements called metals [1]. Additional compounds includes reference to certain light anions in ionic or covalent bonds. often encountered in conservation are and trace metals with an inference to The resulting metallic compounds also listed. The guide is not definitive toxicity. An example of the ambigu- can result in very different proper- or all-inclusive; it is meant to be used ity of the term heavy metal is that of ties of solubility and toxicity [5]. For in conjunction with other resources. molybdenum, a heavy but essential example, trivalent chromium, Cr (III), Complete information about each of AMERICAN INSTITUTE FOR CONSERVATION OF HISTORIC AND ARTISTIC WORKS • 1156 15TH STREET NW • SUITE 320 • WASHINGTON, DC 20005 • (202) 452-9545 • FAX (202) 452-9328 • WWW.AIC-FAIC.ORG their properties, toxicity, and specific tive to semi-quantitative. Some tests easily be used in storage rooms and compound or additional occupational are available in pre-packaged test kits. exhibition cases, as well as on-site for exposure levels can be found in MSDS Spot tests can be destructive or non- field archaeology. sheets, OSHA and NIOSH publica- destructive to the object or surface Inductively Coupled Plasma tions, and other health and regula- being tested depending on the method Spectroscopy (ICP) - Conducts mul- tory governing agencies found on the used. They all involve chemical reac- tiple elemental analyses using a tiny Internet and listed at the end of this tions and need to be conducted in a sample that must be dissolved for the guide. All health and safe handling safe controlled environment whether analysis (a destructive technique). Laser guidelines and hazardous waste disposal in the laboratory or in the field by Ablation-Inductively Coupled Plasma- should be followed as outlined by the trained personnel. Proper waste dispos- Mass Spectrometry (La-ICP-MS) various governing bodies; appropriate al guidelines for hazardous waste gen- models have the capability to analyze personal protective equipment (PPE) erated from the test procedure should certain whole objects. The instru- should be used as described in OSHA be followed [7, 8]. ment yields highly accurate quantita- regulations with particular attention tive results for low levels of elements. paid to the use of respirators. It is an excellent tool to crosscheck Analytical Instruments semi-quantitative to quantitative results Hand-held X-ray Florescence of the hand-held XRF [9]. ICP is a Detection Methods Spectrometry (XRF) - A surface tech- laboratory procedure that must be The appropriate testing method nique, the XRF analyzer conducts conducted by qualified personnel [7, to use for the detection of a spe- multiple elemental analyses and is 10, 11]. cific heavy metal will depend on the considered to be non-destructive to Atomic Absorption Spectroscopy answers to some key questions: the object. It can be used with swabs, (AAS) - Analyzes one element at a • What do you want to know and wipes, or in direct contact with the time using a tiny sample that must be why? surface. The instrument yields quanti- dissolved for the analysis (a destruc- • What is the material type of the tative results for modern metal alloys tive technique). The instrument object to be tested? or soils based on approved NIST yields highly accurate quantitative • Can a sample be taken or must the industrial standards and calibrations results for low levels of elements. test be non-destructive? for which the instruments were made. The use of High Performance Liquid Regardless of the testing method, Results on archaeological metals and Chromatography (HPLC) in conjunc- test results on homogeneous samples glass substrates range from qualita- tion with AAS analysis (used as the are usually indicative of the entire tive to quantitative; results on organic detector) can provide speciation of object, however, results on heteroge- substrates are presently qualitative, but the sample [12.] AAS is a laboratory neous samples (such as organic sub- with appropriate reference materials, procedure that must be conducted by strates) are indicative of the specific instrument calibrations may be able qualified personnel [7, 10, 11]. test site/sample only. Quantitative to offer semi-quantitative ranges. The Spark Emission Spectroscopy - A results are relevant only for the sample instrument is easy to use but spectrum destructive technique that tests mostly or site tested. and data are complicated to interpret, solids and is good for bulk constituents especially on organic substrates because [7]. the data alone cannot be relied on for Wet Chemical Techniques - Spot Tests accurate results and spectrum must Samples must be dissolved (destructive Spot test procedures are relatively be interpreted. Trained personnel are techniques). Wide variety of possible reliable indicators of the presence of necessary for application and accurate techniques, titrations, ion-specific residual surface chemicals. They can interpretation. The hand-held XRF electrodes, etc; may be very useful provide results ranging from qualita- is an excellent screening tool and can depending on the analyte and levels to be analyzed [7]. List of Acronyms Acronyms used in the chart and references: Ion Chromatography - Low lev- CAS: Chemical Abstract Service (chemical For a comprehensive lists of acronyms, els (range of 0.1 ppm) of multiple ions health agencies and governing bodies refer to registry number) MSDS: Material Safety Data Sheets can be determined giving quantitative the following websites: PEL: Permissible exposure limit - OSHA regu- results. The samples must be dissolved ACGIH: American Conference of Govern- lated concentrations mental Industrial Hygienists, www.acgih. making it a destructive technique [7, TLV: Threshold limit value - ACGIH sug- 10]. org gested concentration guidelines CDC: Center for Disease Control and Preven- TWA: Time-weighted average - NIOSH rec- tion, www.cdc.gov ommended exposure limits (RELs) DHHS: U.S. Department of Health and Hu- ppm: parts per million (conversion factors: Health and Safety man Services, www.os.dhhs.gov parts of vapor or gas per million parts of EPA: U. S. Environmental Protection Agency, Unlike industrial workers who contaminated air by volume at 25ºC and 1 are more likely to encounter higher www.epa.gov atmosphere) OSHA: Occupational Safety and Health Ad- mg/m3: milligrams per cubic meter (conver- doses of potentially hazardous materi- ministration, www.osha.gov sion factors: milligrams of vapor or gas per als resulting in acute exposure [13], NIOSH: National Institute for Occupational cubic meter of contaminated air at 25ºC museum workers are more likely Safety and Health, www.cdc.gov/niosh and 1 atmosphere) to be exposed to low-level doses of 2 AIC NEWS, November 2008 heavy metals over an extended period tions listed for the product. Dispose returning it to the store room [8]. All of time, resulting in chronic health of containers and unused contents in pertinent PPE should be used through- problems. Heavy metal exposure in accordance with federal, state and local out the process. the environment along with that from requirements [16]. Laboratory safety *The specific time interval is unknown museum collections and buildings is protocol should be followed. MSDS as it relates directly to the level of airflow and of particular concern to museum pro- documents must be on the premises other factors in the room. Air quality tests can fessionals involved in emergency and in the lab for each substance present. be conducted to determine the time frame using disaster rescue and recovery efforts. Unless a substance is known to not a Jerome 431-X Mercury Vapor Analyzer and Health and safe handling guidelines for be hazardous, it should be treated as a Lumex RA-915+ Multifunctional Mercury specific metals and their compounds though it was hazardous. analyzer [8]. have been developed by national and Documentation- All test results, international governing health and suspect hazards and known archival environmental agencies and are read- information should be documented A Specific Note About ily available in electronic form and (written, photo, analytical test results) Arsenic as Arsine in numerous hardcopy publications.