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I know this should probably be posted in a chemistry exchange, but I figured the parts are pretty standard electronics equipment that the question might be more relevant here.

So a couple of breadboards had been lying in a box with a rubbered aligator wire sandwitched between. They've been there for maybe a month untouched. No other chemical or electricity has been present and only ambient heat (hot summer but 30°C tops here in Sweden). I'm pretty shocked that the plastic of these two different styles of breadboards both got so messed up simply by touching this rubber:

enter image description here

Should I be concerned? Is either the plastic or the rubber dangerous to me?

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    \$\begingroup\$ The covers on the clips are a flexible plastic, not rubber. \$\endgroup\$ – Peter Bennett Aug 23 '18 at 14:57
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    \$\begingroup\$ It looks to me that the "melted" zones are actually additive. By that I mean the breadboards themselves don't appear melted, but it looks more like something clear was deposited on to them. Perhaps there is only a thin layer at the deposition site of the breadboards that has deformed. Can the stuff be scraped off? \$\endgroup\$ – Bort Aug 23 '18 at 15:43
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    \$\begingroup\$ @Bort sorry, I guess the pictures aren't clear enough, but it's actually deep dents, just like you would have put the soldering iron there. No deposits. \$\endgroup\$ – Viktor Hedefalk Aug 23 '18 at 15:55
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    \$\begingroup\$ Your photo is of good quality. Maybe it's just an illusion, but it really does seem to me that the melted areas are risen above the breadboard. (Each spot looks convex, not concave). The blue strip on the white board appears to be straight and non-smeared under the clear melty stuff. \$\endgroup\$ – Bort Aug 23 '18 at 15:59
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    \$\begingroup\$ This exact thing happened to me. I stored some cheap alligator jumpers in an acrylic box that a "build your own PWM" kit came in, and the hoods on the clips "melted" the acrylic. \$\endgroup\$ – JPhi1618 Aug 24 '18 at 15:47
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"Melts" isn't the correct term here -- that would involve heat.

The vinyl boot on the alligator clip contains a solvent called a plasticizer that helps keep it pliable. However, it is volatile and its outgassing has also affected the plastic used in the breadboards.

The solvent is a volatile organic compound, and is probably dangerous if concentrated sufficiently, but at the low rate that it outgasses in a reasonably ventilated space, it is generally considered safe.

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    \$\begingroup\$ Updated melts to "melts" :) Thanks for clarification! \$\endgroup\$ – Viktor Hedefalk Aug 23 '18 at 14:50
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    \$\begingroup\$ As a side note, plasticizers is what gives new cars that new car smell, so if one is genuinely concerned about it being dangerous, the first thing to do would be to stop driving new cars. \$\endgroup\$ – Dmitry Grigoryev Aug 24 '18 at 7:52
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    \$\begingroup\$ @DmitryGrigoryev The smell cannot be attributed to plasticizers exclusively. Car manufacturers also add scents or fragrances intentionally (... possibly to overpower the smell of plasticizers). \$\endgroup\$ – Ian Aug 24 '18 at 8:30
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Interesting. The PVC (Polyvinyl Chloride) composing the alligator clip insulator is only part PVC chemically, a good percentage of it is plasticizer. That's what you smell from something like a swimming pool liner or beach ball, not the plastic but the plasticizer. PVC can be a majority plasticizer by weight if it has to be very pliable.

It's likely that whatever chemical they used in the insulator plasticizer does not get along with the plastic in the breadboard and has dissolved it a bit. The heat will have contributed to the issue and how quickly it occurred.

Personally, I would not worry too much about it being toxic or anything- however the EU has been paying a lot of attention to regulating plasticizers and other chemically active additives such as fire retardants.

ABS (often used on cheap breadboards) is not resistant to phthalates- the traditional PVC plasticizer- according to this chart. From my above link:

In Western Europe about one million tonnes of phthalates are produced each year, of which approximately 900,000 tonnes are used to plasticize PVC.

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  • \$\begingroup\$ I wonder if this is related to the problem where the sticky label on a power cord starts to become unstuck and leaves a very slimy residue on the cable (any anything it touches). Presumably the rubber insulation on the cable will have plasticizers in it. \$\endgroup\$ – Wossname Sep 5 '18 at 9:45
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The most commonly used plasticizers are phthalates and they are probably not good for you, and especially children

Several phthalates are "plausibly" endocrine disruptors.[24] The long-term health effects of exposure to endocrine disruptors, such as phthalates, are unclear.[25]

Authors of a 2006 study of boys with undescended testis hypothesized that exposure to a combination of phthalates and anti-androgenic pesticides may have contributed to that condition.[26]

A scientific review in 2013 came to the conclusion that epidemiological and in vitro studies generally converge sufficiently to conclude that phthalate anti-androgenicity is plausible in adult men

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    \$\begingroup\$ Generally wash hands after handling cables. This includes household power cables. \$\endgroup\$ – Peter A. Schneider Aug 24 '18 at 11:46

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