The defendant was accused of the shooting death of his wife. Police administered gunshot residue samplers to the defendant's hands and objects that he likely came into contact during the interval from the shooting to his arrest. The examination of the samplers by scanning electron microscopy/element analysis showed no particles of gunshot residue, except the sampler of a set of keys from the defendant picked up lead particles. The criminalist called these particles “consistent with gunshot residue.” There were no control examinations (i.e., testing other sets of keys) made. As will be seen, it is unlikely that the source of the lead particles found by the criminalist originated from a firearm.
In 1999 the California State Attorney General's Office filed a complaint against thirteen lock and key manufacturers under California's Proposition 65 due to lead in their keys. The basis for this lawsuit was that the brass keys manufactured by these firms have from 1.5 to 2.5% lead content. An agreement was reached with the defendants in 2001. “Most common keys are made from brass that contain 1.5 to 2.5% lead, but the defendants agreed to no longer make keys with more than 1.5% lead. Some keys, including many car keys, are steel and contain only trace amounts of lead. Other keys are made from nickel-silver, or plated with nickel-silver, and do not give off significant amounts of lead”.
By the manufacturers apparently saying that the lead is “alloyed” with the brass (copper + zinc) of the keys implies that the lead is homogeneously distributed throughout the brass. An internet search has failed to uncover any information as to the nature of the lead association with the key brass. Why is this determination important? If the lead component of keys is heterogeneously distributed (i.e., there are areas on key surfaces that have concentrations of lead), normal key wear might expose high-percentage composition lead particles to the handler.
Not only does lead in keys expose handlers to this toxic metal, but the locksmith/key makers are receiving particularly heavy exposures. Key makers appear to have a health risk many times that of the key user due to continuous lead exposure from the grinding of key brass. Kondrashov et al. (Anesthesiology, 2004; 101:A1396) tested six professional locksmiths and six control volunteers for bone and blood lead and concluded that “locksmiths are chronically exposed to lead.”
Another issue perhaps even more serious is the propensity of parents to give babies and toddlers rings of keys as toys. Some children become so enamored with keys that parents request used keys from lock and key stores.
Samples were taken of dust and metal debris around three key grinding machines with the standard adhesive samplers used for gunshot residue sampling. A house key, in continuous use for approximately 25 years, was also examined. The samplers and the key were analyzed in the scanning electron microscope and lead was found by backscatter electron imaging and identified by elemental analysis.
Lead was found on the key brass fragments and dust surrounding key grinding machines. Many of the brass shavings from the key grinding machines have a “coating” of lead that appeared to have been molten at the time of deposition. Lead that is “alloyed” with key brass has a heterogeneous distribution (in other words, it is not an alloy): fragments of brass were found that contained not only spherical inclusions but also veins of lead. The friction of the grinding wheel against the key brass generates enough heat to cause the lead within the brass to become molten. Free lead particles were noted in the dust associated with the key grinding machines. Many of these were spherical (they were likely created by heat) and were formed during the grinding process. Thus, a portion of the molten lead likely becomes an aerosol during grinding to be respired by the locksmith/key maker. Aerosolized lead probably is the primary mode of contamination for the locksmith/key maker; the other is imbibing lead via contaminated hands. Remnants of lead on a key after grinding likely remain after delivery to the customer by the key maker. Such lead contamination will expose the handler to a concentration of lead well above that present in older keys.
The 25-year old house key showed deposits of lead on the brass surface and many of these had gaps around the embedded lead. The appearance of these defects in the brass of the key suggest an erosion of either the lead or brass from the interface area. Free lead particles are likely formed in this manner. It appears that a tape lift sampling of keys for gunshot residue analysis dislodge some of these embedded lead particles from the small pits on the key surface. This suggests that old brass keys are a continuous sources of lead particles on the user.
A health risk exists for the entire population, not just the locksmiths/key makers. Small children who are allowed by their parents to play with keys might have significant lead exposure, especially for those children that put keys in their mouths. Long term sucking on keys may be a source of lead that health officials have failed to consider with children who have been found to have elevated blood lead. The consequence of lead in children is well known – brain growth retardation and other health issues.
Gunshot residue samplers from suspects in shooting cases should not be reported as having particles “consistent” with gunshot residue when the only particles found are lead that do not have the metals barium or antimony associated. It is likely that lead particles from keys are ubiquitous in our environment, especially on hands.
As noted, the California State Attorney General came to a settlement with the manufacturers regarding key lead. Part of the settlement was that key manufacturers “…will pay $30,000 to the Public Health Institute to advise pediatricians, child care providers and others about the importance of not letting children play with keys, because of the lead hazard they pose”. The single $30,000 payment was obviously inadequate. I occasionally observe small children playing with keys. Parents of these children are shocked when informed of the lead hazard and wonder why they had not been warned.
This article by Bryan Burnett, M.S.was published in The San Diego Daily Transcript on October 18, 2006 as part of the Forensic Consultants Newsletter. Bryan Burnett is the Principal of Meixa Tech & Forensic Science Consultants Group and specializes in Scanning Electron Microscopy and its application to such things as gunshot residue and asbestos analysis in lung tissue.
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