Mothballs deserve respect

Labeling, while deficient, offers hints to risks.

SAN FRANCISCO I don’t use mothballs — except sometimes to sprinkle down the burrows of animals excavating tunnels beneath the deck floor of my pergola. It’s the most effective stop-work order for wildlife that I’ve found. But I won’t use these stinky crystals inside my home because they scare me. And those fears appear justified, according to Linda Hall of the California Environmental Protection Agency.

Packaging labels on mothballs are helpful in determining safe use, despite some potentially serious omissions, researcher finds. Credit: M. Bernstein, ACS
LABELS OFFER CLUES, BUT… Packaging labels on mothballs are helpful in determining safe use, despite some potentially serious omissions, researcher finds. M. Bernstein, ACS

At the American Chemical Society spring national meeting, here, last week, she spoke about why moth crystals deserve more respect than they seem to get. And if we get sick using them — as some people do — it may be partly our own fault for not following labeled instructions.

The active ingredient in many, para-dichlorobenzene, can poison the liver, skin, and central nervous system — and is a “possible human carcinogen,” according to the U.S. EPA. But product labels don’t say that, Hall pointed out. They merely instruct consumers to use the moth repellent in an airtight container and to air out treated fabrics.

Yet most people I know (including older family members) have no problem sprinkling these crystals in a far-from-airtight closet or a zippered bag stored in the basement. If you can catch a whiff of their sweet scent, the container isn’t airtight.

Most mothball labels also contain a cryptic warning: Avoid contact with skin — and wash any contaminated clothing. Huh? I thought the whole idea of using mothballs was to have their vapors permeate clothing — especially hard-to-wash wools — so that they won’t be attacked by voracious moth larvae.

Clearly, Hall says, the labeling tends to be vague and somewhat schizoid (my paraphrasing). Then again, what’s on the labels may not matter much, she notes, because in her anecdotal experience people are so comfortable using the chemical that they seldom bother reading the fine print on product packaging.

In California, doctors must report when people are sickened by the pesticide. The state database contains 16 instances of known or suspected poisonings. Which doesn’t sound like much, except that “you have to report to a doctor to get into this database,” Hall points out, so “illnesses may be underreported.” Moreover, she says that the system isn’t designed to capture people who may have been sickened by long-term chronic exposure.

And she knows of no comparable national database to tally para-dichlorobenzene poisonings outside California.

At the meeting, Hall noted that sales in her state of moth crystals containing para-dichlorobenzene run around 600,000 pounds per year, of which 99+ percent are purchased for home use. This means they’re applied by people who must rely on the labels for guidance on safe use.

Yet the labels are deficient. They give minimum-effective-use information, but no safe maximums. For agricultural pesticides, safe upper limits are mandatory, Hall noted. That’s one reason a new rule that mothballs do the same “is under consideration right now by our department,” she said.

Labels also don’t explain how long treated fabrics must be aired out to reduce contamination to safe levels. Cal EPA is conducting tests to quantify such airing-out times, she noted. It’s also measuring “exposures that might come from [treated] closets.” Currently, Hall reported, para-dichlorobenzene is sold in some sachets or embedded in padded hangers — products people would likely use openly in closets. Her agency will also be calculating exposures that might occur when moth crystals are used according to label instructions.

Until such data are in, she recommends that people stick to using no more than the minimum effective amount: one pound per 50 cubic feet. She also recommends only using these products in tightly sealed containers and airing treated goods in well-ventilated areas — outdoors, when possible.

 At the meeting, I asked Hall if any records were kept on pet poisonings. She knew of none. I then mentioned how I came to foreswear para-dichlorobenzene. It was shortly after I had moved to Washington with three cats in tow. One day I heard Phoebe, the shy one, wailing. She was staggering and bumping into walls in a disoriented fashion. When I picked her up, she positively reeked of moth crystals.

The only place I used them was in the basement, inside a self-standing garment box the movers had used. The next day, while scooping the litter, I found her perched atop that garment box.

Out it — and moth crystals — went. Several months later, Phoebe began to waste away and nothing the vet did stalled the process. I mentioned the moth crystals and the vet agreed it was a suspicious — albeit tenuous — link. In short order, Phoebe was dead. And moth crystals never again entered my home.

Hall acknowledges that it sounded like Phoebe had suffered acute intoxication from the moth repellent. In fact, she noted reports of similar neurological symptoms in French teens. They had difficulty walking and riding after using the sweet scented crystals as a source of an inexpensive high.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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