A tale of two mothballs

A recent report out of the New York City poison control center piqued my interest. The case concerned a 44-year old man living independently, albeit with a mild mental retardation, found prostrate in his apartment. Quite a few poison control cases start off heading down a similar road. But this one quickly veered off in an unexpected direction. The man in question had developed bizarre behavioral symptoms over the two weeks leading up to his collapse; on medical examination, he had abnormal body movements, demonstrated impaired thinking, and wafted off an odd, aromatic odor. When an MRI scan documented a form of severe central nervous system deterioration called leukoencephalopathy, the patient's doctors were at a loss to explain the underlying cause of his pathology. The source of the devastating brain injury eventually came to light, however: mothballs.

In a morbid twist on the old vaudeville joke about the man sent by his wife to see the psychiatrist because he likes pancakes (Therapist: "Well, I like pancakes, too" Patient: "Really? You must see my collection - I have 7 trunks full"), the patient liked mothballs. In this case, in addition to ingesting them, "liking" meant compulsively heating mothballs over a flame and inhaling the aromatic fumes released. Chemically speaking, heavy exposure would be easily generated in such a scenario. The chief molecular constituent of the mothballs in question, the dominant form on the U.S. market today, is the toxicant paradichlorobenzene (PDCB).

When I first trained in medical toxicology, we were taught to be big boosters of PDCB, because it was replacing the previous king of the mothball hill, the chemical naphthalene. Naphthalene is acutely toxic if ingested, among other effects causing a dangerous impairment of the blood's ability to hold on to oxygen in the lungs and deliver it to sustain the body's tissues. In contrast, PDCB can be fed generously to rats and mice without much effect. Both products look alike and both are prone to be mistaken for candy by young children rummaging through drawers or closets with this hidden treasure concealed within. This is common enough that poison specialists behave developed a simple test to differentiate between the two: in a concentrated salt or sugar solution naphthalene balls float, PDCB balls sink.

In the U.S., this mothball high-ball concoction is not likely to be that relevant, except perhaps to the storyline of some future episode of a TV forensic crime drama. That's because naphthalene mothballs are largely off the domestic U.S. market. Largely, but not entirely: the Federal EPA still licenses it for home use, noting that by 2013 manufacturers have "agreed to take product stewardship steps to ensure that products are packaged in a way that would discourage children from eating the product" (http://www.epa.gov/pesticides/reregistration/REDs/naphthalene-red.pdf). Of course, even if the EPA banned it, this would not solve the problem of illegal imports. Early in 2009, the EPA identified an Oakland, California importer bringing in illegal naphthalene mothballs from Taiwan. The EPA noted that this posed "a serious threat to human health, particularly children's health" (http://yosemite.epa.gov/opa/admpress.nsf/d0cf6618525a9efb85257359003fb6…), levying a slap-on-the-wrist fine of $61,000 for 241 separate acts of product distribution ($253 a pop, slightly less than the $260 fine in Oakland for parking a heavy commercial vehicle in a residential district).

One reason that naphthalene and PDCB are both effective anti-moth agents is that the solid ball gradually gives of gas at room temperature. No special heating required. Indeed, at first I presumed that this made the exposure scenario in the case of the flame-generated PDCP inhaler so extraordinary as to be one-of-a-kind. Unfortunately, this is not the case. The medical literature is peppered with multiple reports of PDCB neurological toxicity, including the white matter destruction of leukoencpheplothy. This has been noted in persons abusing PDCB by inhaling the substance unheated or simply by ingesting it. As alarming, a recent laboratory study found that PDCB administration in both rats and mice led to hormonal effects, reduced sperm production, and altered sperm morphology.

PDCB, unlike naphthalene, also is used widely in toilet deodorant blocks. For that reason the EPA has also considered its potential for wider environmental release through water contamination. On November17, 2010 the EPA announced a new list of chemicals to be included in laboratory screening for hormonal effects such as those seen in the PDCB rodent study (http://www.epa.gov/endo/pubs/prioritysetting/draftlist2.htm). Such potential effects were not assessed in PDCB's current registration as an approved pesticide, but then again, leukoencephalopathy was not considered either. Six days after release of the new testing list and two days before this last Thanksgiving, on November 23, the EPA seized an illegal Chinese import shipment of nearly 5,000 invitingly-packaged PDCB-laden "Fuji Lavender Moth Tablets."