I've been eating a lot of watermelon for the past few months (all
purchased from the same source), and I've noticed that afterward my
mouth sometimes tastes like mothballs. I'm wondering if there's a
connection. Are trace amounts of naphthalene (the poison used in
mothballs) naturally found in watermelon?  Can watermelons become
contaminated with naphthalene?  If not, why might I be experiencing
this mothball taste?  (There are no mothballs in my home.)

Dear ltmickey-ga;

Thank you for allowing me to answer your interesting question.
Naphthalene is not a naturally occurring chemical in watermelons. The
fact that you taste it in yours is concerning indeed. It?s hard to say
why, in your particular case, you may taste this chemical but let?s
take a look at what is published about it:

Naphthalene, the chemical found in common mothballs, is occasionally
used in agricultural industries as a fumigant, insecticide or pest
repellent. Under certain circumstances (particularly over-zealous or
excessive use) vegetables can absorb enough Naphthalene for unsafe
levels to be present.

EVAPORATION OF FUMIGANTS
http://www.fao.org/docrep/X5042E/x5042E02.htm
 
Naphthalene is, however found naturally in the environment in fossil
fuels like coal or oil. Burning tobacco or wood also naturally
produces naphthalene. Naphthalene binds weakly to soils and sediment
and it easily passes through sandy soils (like soil in which
watermelons are typically grown). In addition, it is rare in high
concentrations, but naphthalene has been known to accumulate in ground
water so pockets of contaminated water could, in theory, contaminate
water dependent vegetables like a melons. The chemical is also found
in plastics like polyvinyl chloride (PVC), for example. It would be
more reasonable, I suppose, to suspect that the chemical might have
gotten into your vegetables via a particularly high concentrated
growing area (the soil in particular) from which the watermelons
originated, either because the area was manually fumigated by the
grower or because the concentrations are higher due to naturally
occurring oils, coals or substantial wood, oil, coal or plastic fires.

NAPHTHALENE FACT SHEET
http://www.epa.gov/epaoswer/hazwaste/minimize/factshts/napthal.pdf

You can get more information about this document from the Agency for
Toxic Substances and Disease:

Agency for Toxic Substances and Disease
Registry Division of Toxicology
1600 Clifton Road, N.E., E-29
Atlanta, Georgia 30333

You can also get information about the potential hazards of ingesting
Naphthalene from the US Environmental Protection Agency:
http://www.epa.gov/iris/subst/0436.htm

Naphthas (distilled spirits from coal, wood and other products) are
sometimes used to treat and preserve wood, rubber and other
manufactured goods. Technically gasoline, kerosene, diesel fuel, etc
are all considered ?Naphthas?. If the melons containers were recently
treated or the melons in some other way have been contaminated with a
naphtha this might also explain the absorption and subsequent taste
you are experiencing.

MATERIAL DATA SAFETY SHEET: NAPHTHA
http://www.rectorseal.com/msdsshts/heatingprdcts/msdsaquasorb.html



I hope you find that my answer exceeds your expectations. If you have
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prior to rating the answer. Otherwise I welcome your rating and your
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near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad-ga ? Google Answers Researcher



INFORMATION SOURCES

ECO-USA
http://www.eco-usa.net/toxics/naph.shtml



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Thanks for the quick and thorough answer!  This information was very helpful.

I found this connection:

http://www.hort.uconn.edu/ipm/homegrnd/htms/8racoon.htm

Raccoons damage watermelons by digging a small hole in the melon and
then hollowing and raking out the contents with their paws.

[edit]

Repellents

A variety of materials have been tried to repel raccoons with no
proven effectiveness, including blood meal, dog feces, mothballs and
dirty laundry. Mothballs (naphthalene or paradichlorobenzene) are
relatively ineffective in an open air situation, but these have been
shown to have temporary effectiveness in repelling raccoons from
enclosed spaces such as sheds, attics or crawl spaces.

Aren't mothballs made from paradichlorobenzene?

Mothballs can be made from either paradichlorobenzene or naphthalene.

Here is a web site saying paradichlorobenzene is more common today:

http://paradichlorobenzene.iqnaut.net/

I think you can still get the naphthalene ones; at least, I thought
the last batch I bought smelled like naphthalene - but, then, I've
never compared the two smells and may be imagining the mothballs were
naphthalene.