She works in a book factory, and uses methylene chloride as a solvent, under a hood.
She is breastfeeding, and worries that this will contaminate her breastmilk.

Methylene chloride, in high concentrations, can depress the central
nervous system, producing drowsiness, nausea, tingling and numbness
(these would be extreme situations).  Most people can smell it at low
concentrations and avoid such excessive exposures.

It has not been shown to cause cancer in humans exposed to vapors in
the workplace.   However, breathing high concentrations of it for long
periods did increase the incidence of cancer in mice.  My opinion is that
this material is not likely to be a carcinogen at the low concentrations that
are likely to occur in a workplace. The Occupational Safety and Health
Administration proposes to reduce the current occupational exposure
limits to methylene chloride in air. The limit would go from 500 ppm to 25
ppm for an 8-hour workday.

From what little information I have, it appears that methylene chloride
would not accumulate to a great extent in breast milk.  Nothing like dioxin
or other chlorinated chemicals that are typically associated with breast
milk as impurities.

 As long as she is following established industrial hygiene practices,
avoiding any unnecessary exposures, I think she should be OK.  If she
has any reason to believe that her exposure are greater than what
OSHA is recommending , she should talk to her supervisor.

I hope this helps!!

~~ Nancy Penney
Houston (Katy), TX