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I don't know if this is the right place for my question. Anyways: We work with cadmium plated nickel-base connectors. These are "Amphenol SJRT series" connectors.

See this image:

image

Catalog

The plating we use: "Olive Drab Cadmium Plate Nickel Base"

I want to know if this metal coating is generally safe to handle on a daily basis.

I've noticed that the green coating is gradually worn out.

I only have some rudimentary chemistry knowledge and the only thing I know is that cadmium is a toxic metal.

Is it in a safe compound when plated on nickel? I read "cadmium plated nickel base" as a cadmium layer on top of nickel. So it is no compound, right?

How does cadmium behave when touched with bare skin? Is it somehow solved by acids / fat / other stuff?

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    \$\begingroup\$ Is there a reason you need to be handling the contacts to a significant degree? The use I've heard of for cadmium plating is to make contacts more resilient to arcing, so the plating would normally be on device internals and rarely seen by a human. What is your application? \$\endgroup\$
    – K H
    Mar 2 at 9:00
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    \$\begingroup\$ I'm not a toxicologist specializing in heavy metals. I'm basically ignorant. But there is no way I'd work in a situation where I regularly had skin contact with your substance without very clear and comprehensive evidence given to me showing why it is safely handled that way. I'd want the exact mechanisms making it safe explained in detail to me. Not handwaving; no reference to single sources. I'd need to independently agree. Long term exposure not only leads to cancer but to organ failures throughout the body, everything from bone, central and peripheral systems. Nothing escapes it. \$\endgroup\$
    – jonk
    Mar 2 at 9:05
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    \$\begingroup\$ @GNA Someone saying that to me would get a request to "prove it." Obviously, that's just a claim by fiat. If they know why it is true, then they should be able to sit down with you and teach you what they know and why they know it, with references to experimental results. For example, ask your so-called safety dude to provide specific studies on the solubility of each specific compound in the goop in biological fluids. If they cannot do that much, you already know they are lying or else are ignorant and not to be trusted. Solubility here isn't sufficient to know, but it is certainly necessary. \$\endgroup\$
    – jonk
    Mar 2 at 9:27
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    \$\begingroup\$ @GNA Get used to doing some searching on NCBI and get informed. For example, start here: Cadmium and Cadmium Compounds. Then ask the safety dude to show evidence of what compounds are in the stuff and what happens to those compounds as they are exposed to oxygen, light, etc. It's likely to be a veritable soup. But if they can claim all this stuff is safe, then they should be able to list everything out and explain how they arrive, both initially and during processing. I hate it when someone says "compound"="safe" and then hopes that's enough. \$\endgroup\$
    – jonk
    Mar 2 at 9:41
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    \$\begingroup\$ I want to thank you for bringing this to my attention by the way as (despite a background in chemistry) I had not spotted that some connectors I ordered recently are in fact chromate-on-cadmium plated. I think I either used the part number I was given or chose the cheapest one off the website that matched the pin spec, and as I don't regularly deal with mil-spec kit it never occurred to me that they might be coated in something toxic (!). I will be flagging this up to my employer and colleagues. \$\endgroup\$
    – nekomatic
    Mar 16 at 12:38
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4th year chemistry student here. I have experience with dangerous chemicals, regulations and best practices as I am exposed to them on a weekly basis. Moreover I have studied and formulated my years winning zinc corrosion protection paint blend for Hempel Incorporate.

I've noticed that the green coating is gradually worn out.

  • This is definitely not good, 'olive drab' is a chromate finishing. This type of chromium is hexavalent and is very carcinogenic, genotoxic in fact. You are not working in the most exposed industry with regard to this health risk, but still, you wouldn't want 'olive drab' hands to come into contact with your mouth,eyes or nose, especially on a daily basis.

-https://www.cdc.gov/niosh/topics/hexchrom/

-https://en.wikipedia.org/wiki/Hexavalent_chromium#Toxicity

-https://www.finishing.com/110/07.shtml

-https://www.serdp-estcp.org/asetsdefense/Clean-Alternative-Information/Cadmium-Plating-Alternatives

Is it in a safe compound when plated on nickel? I read "cadmium plated nickel base" as a cadmium layer on top of nickel. So it is no compound, right?

  • It is plated and with repeated use/handling the cadmium layer could potentially rub off on hands and if those hands are not cleaned before interacting with the respective mouth, nose, eyes, etc., then one could consider it unsafe. Moreover I would not say its safe relative to other coatings.
  • Correct, it is not a compound ( bonded at the atomic level), more a lamination and thus more likely to "rub-off" as the resulting bond isn't the strongest .

https://en.wikipedia.org/wiki/Electroplating

How does cadmium behave when touched with bare skin? Is it somehow solved by acids / fat / other stuff?

  • Hand sweat consists mostly of water and trace amounts of urea, minerals and lactic acid. I would say that lactic acid is a moderate acid with a pka of approx. 3.5, but we are talking trace amounts in sweat. So cadmium doesn't really react with 'hand chemicals'. But after repeated handling this will likely be a different case, in conjunction with the above mentioned mechanical "rub-off". Watch out for exposure to stronger acids, especially if those connectors are in a oxygen scarce/vacuum environments.

https://en.wikipedia.org/wiki/Perspiration

In conclusion, these coatings becomes a real health risk when they enter the body, especially if inhaled, which is not the case here. They could however come into contact with eyes, nose, mouth,etc. through hand contact so be very wary of this. The olive drab rub-off is alarming. So in answer to your main question, I would say no - it is not generally safe.

The use of cadmium plating is understandable; it provides great sacrificial plating for corrosion protection, great conductivity (for grounding, emi shielding etc.), it can operate at aerospace temperatures, great lubricity, and excels with regard to other connector performance requirements - all at a great price point.

Initially I was wondering why zinc plating wasn't used but reasoned that this was due to aerospace requirements prioritizing the above-mentioned properties. However, I just read that Boeing already found a zinc plated alternative some 30 years ago (1992). Moreover it seems that the EU, SAE (society of Automotive Engineers), Raytheon and other agencies have found alternatives and are moving away from cadmium plated hardware. SAE state that Electroless Nickel Teflon is closest alternative. See the following links for more alternatives.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a602494.pdf

https://www.turi.org/content/download/9287/16338/file/Alternatives%20to%20Cadmium.Misiaszek.Aerospace%20Defense%20Conference.24%20September%202013.pdf

https://dev.caltechplating.com/nickel-cadmium-diffused/

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  • \$\begingroup\$ Here is the Raytheon review link, it somehow broke in the original post. - turi.org/content/download/9287/163383/file/… \$\endgroup\$
    – J.Doe
    Mar 11 at 12:24
  • \$\begingroup\$ Thanks for your answer. I'm currently on it to get the information I need to get rid of these connectors. We don't need all the fancy features these coatings offer. We use them indoors -_-. Anyways. Thanks a lot. Now I know that I shouldn't let go of this topic. \$\endgroup\$
    – GNA
    Mar 11 at 12:42
  • \$\begingroup\$ Your welcome, thanks for the acceptance! I agree, that would be a really good idea. I see - well then it's really an unnecessary risk to be exposed to. Good, I would also consider their use as unacceptable! \$\endgroup\$
    – J.Doe
    Mar 11 at 15:03
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Here is the risk assessment from a European supplier of such connectors. I suggest seeking out similar documents from other makers (and, in general, familiarizing yourself with MSDS (Material Safety Data Sheets) for things you are working with (especially liquids such like). Although a bit technical, they are intended to give information on risks to the users. In many places you can refuse work that is dangerous without fear of losing your job.

Risk Assessment Substance Name: Cadmium CAS

Number: 7440-43-9 SVHC Number: ED / 69 / 2013

The use of cadmium as plating finish still has an important role in safety critical applications. As plated surface on component, cadmium does not represent a risk to health. Cadmium is not easily absorbed through the skin, so handling cadmium plated products exposes no risk to the user. The main risk to health is cadmium dust or vapour, which can be generated by machining welding or polishing. The main route of entry into the body is via inhalation followed by ingestion. If it corrodes, cadmium forms a white crystalline cadmium salt deposit on the surface of the plating and this can represent a health risk of not handled properly. The deposit may enter the body through inhalation if it becomes airborne or ingestion. Cadmium and the compounds formed when it corrodes are toxic by ingestion, acutely toxic if inhaled, may cause cancer and are suspected of being able to cause genetic defects, damage fertility and to be harmful to the unborn child

I'm not sure I agree with the logic behind the "no risk to the user" statement above. In actual use the connectors sometimes have a bit of material flaking off, especially when mated and unmated many times. So I would definitely wash my hands after handling them and not be eating at the same time (similar to working with lead solder paste).

We had to use cadmium plated fasteners in aircraft applications, and always kept those fasteners properly labeled and separated from ordinary chromated or whatever fasteners.

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This is really for informational purposes, I'm not implying that anyone should do anything, use at your own risk. I just want to give an idea of what exposures are acceptable.

Is it in a safe compound when plated on nickel? I read "cadmium plated nickel base" as a cadmium layer on top of nickel. So it is no compound, right?

If it's nickel plated, then the odds of you contacting cadmium are significantly reduced if not zero.

How does cadmium behave when touched with bare skin? Is it somehow solved by acids / fat / other stuff?

Usually sweat contains salts which react with metals (I have no idea if this is the case with cadmium, but it happens with other metals, I don't know the actual reactions) but the salts get into your skin (as with copper which your body can handle larger amounts).

Skin is the not recognized to be a large source of cadmium exposure by those who study cadmium exposure, that being said if your worried about it and want to be risk free put on a set of gloves when handling it and it will reduce your exposure.

Hazards to worker (as well as public) health presented by cadmium compounds in various processing steps vary as a function of compound specific toxicity, exposure mode and physical state of the compound. Differences in toxicity among various cadmium compound were highlighted in the previous section. Possible exposure pathways include inhalation, ingestion . and dermal absorption. In production facilities, workers may be routinely or accidentally exposed to cadmium compounds through the air they breathe, as well as by ingestion from hand-to-mouth contact. Of theses two pathways, inhalation is probably the most important because of the larger exposure potential, and higher absorption efficiency of cadmium compounds through the lung than the gastrointestinal tract. In general, absorption through the skin is not recognized to be a large source of exposure to cadmium compounds.

Source: Environmental, health and safety issues associated with the manufacture and use of II–VI photovoltaic devices

Granted it all depends on your risk level. I would probably put on gloves if I were handling cadmium parts.

Cadmium is in many places though, and most of us are exposed to it on a daily basis in really really small amounts. Toxicity happens if a person is exposed to too much of a substance.

In bottled water cadmium is allowed up to 5ng/L, also the limit of toxicity imposed by the Agency for Toxic Substances and Disease Registry is 0.1ug/kg/day (so a 100kg person could be exposed to 10ug/day)

Chronic durational oral minimal risk level (MRL) of 0.1 µg/kg/day of cadmium based on its renal effects. Source: ASTDR What Are the U.S. Standards for Cadmium Exposure?

Who knows how much you'd get by touching a cable connector, I would think it's below that level, but again if you want to reduce your risk wear gloves.

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This is a complicated subject, but I'm going to take a shot...

As with many things used in the electronics industry, cadmium plated components aren't without risks. The highest risk being the industries that use the materials in high concentrations and large quantities. It is important though, to consider route of exposure as well as if the exposure is significant compared to background exposure. Cadmium is a naturally occurring element and is present under many circumstances in the natural environment.

As with all electronics components handling, you should always wash your hands after handling them, especially before eating and not touch your eyes or mouth while handling electronic components.

Cadmium exposure from those connectors is probably well below detection limits and you would need to be exposed in the worst case scenario for long periods of time to see any effect. Cadmium in high doses through ingestion tends to accumulate mostly in the kidneys causing renal tubular dysfunction and is thought to contribute to hypertension. You would probably need to lick 8-10 connectors a day to get a significant dose. Please don't do that. This type of connector has been used in naval electronics and avionics for many decades and though we haven't made any direct connections to contact exposure causing disease, I don't think it could be completely ruled out. The risk of handling cadmium plated parts is very low if you practice good hand hygiene.

Personal safety is an important consideration and everyone should spend a bit of their time understanding the environment in which they find themselves. Don't rely on an industry that uses a chemical to tell you how dangerous that chemical is. At the same time, it's important not to go overboard with demonizing any one safety concern. Understanding the molecular consequences of everything you are exposed to is nearly impossible.

Luckily, we are provided with an array of protection mechanisms that can help us tolerate certain exposure levels to chemicals. Cadmium in small doses up-regulates a protein called metallothionein which can bind the cadmium and prevent toxicity. Making metallothionein can be problematic to folks that have cysteine related disease and they need to be more careful with metal exposures of all sorts.

I'm pretty sure someone could write a book on this and maybe they have already. The problem is that most of us don't have time to read the thousands of volumes it would take to understand every molecular interaction that may be dangerous to us so we often rely others to tell us one way or the other. It's hard to say how well we've been served by this method of learning, but it allows us time for pursuits other than constant reading.

In the end, you need to make your own assessment of the risk vs. reward. What's right for one may not be right for the other. We each need to find our own balance that allows us to sleep at night and live our life without thinking we need to be locked in a bubble, but not become so complacent that we seal our fates with ignorance. It's a fine balance.

This document may be a useful resource to understand the relative risk of cadmium exposure. You can also visit the pprc.org website for other valuable resources.

Edit: It's important to note that the corrosion plating used on connectors is very thin, usually measured in nano meters or microns at best. Being so thin, they need to be very stable in order to maintain the characteristics of the coating. If the entirety of the coating were to just "rub off" then the coating would be useless. These coatings are very stable under normal use and it's the reason that they last for decades without corrosion.

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  • \$\begingroup\$ Note that concerns about toxicity of working materials started to rise only maybe two decades ago. The kind of plugs in question here have been in use since the 1960s or so, and just the aircraft industry is very slow in adapting to change - if they have something that works reliably. And they don't want to change something, because that's costly. \$\endgroup\$
    – PMF
    Mar 9 at 14:46
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I'm certainly not an expert for health and safety topics but there is for example a

guideline by the Occupational Safety and Health Administration (OSHA)

which states:

Permissible Exposure Limit (PEL). The employer shall assure that no employee is exposed to an airborne concentration of cadmium in excess of five micrograms per cubic meter of air (5 µg/m³), calculated as an eight-hour time-weighted average exposure (TWA).

How much is 5 µg per cubic meter? It's one cadmium particle of 51 µm size per cubic meter or just 562 pL of volume.

I'm not sure how thick the plating is on those connectors, but this manufacturer starts around 5 µm thick plating. With that you'd need a particle of around 0.3 x 0.3 mm (or multiple to sum up to that).

The risk assessment will of course depend on how quickly you are seeing this degradation in the plating. There is this surface treatment manufacturer who states:

It’s not as useful in acidic environments: Cadmium is particularly susceptible to acidic environments. Cadmium’s touted corrosion resistance is practically nonexistent in acidic environments, making cadmium useless in certain applications.

As our skin is mildly acidic I wonder if that is the main source for the seen degradation.

So for me it doesn't sound like something you'd want to handle every day if it is avoidable. And it sounds like it is avoidable as there are other plating or coating options around which do not use cadmium and might work just as well. But in special applications it might not. If it is not avoidable using gloves while handling the connectors would help reduce the risk.

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