Replacing lead weights with US nickel coins

[pwoolf]

For the past few years I've been using US 5 cent nickels instead of lead as a soft dive weight. I often hear that we have to use lead in diving because all other options are too expensive (stainless, tungsten, gold, platinum, etc). But cupronickel (the alloy used for nickels) has a long history in marine use as ship hulls and impellers.

How I use them: Nickels work like a nontoxic version of lead shot, so I use them in a zipper belt (as in picture) or in the velcro soft pockets used for lead shot (you can new buy empty ones online). I find that I can easily fit 4 lbs of nickels into a 4 lb shot bag, so they take up a similar volume. For reference, 1 lb of nickels is about 91 nickels. I've even made a handy calculator to estimate the number of coins (US and global) and their approximate value in USD for any weight you want.

Some questions and answers people have asked about using nickels:
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Q: Cupronickel is not as dense as lead, so can it be used as a dive weight?

Yes, cupronickel can be used. It isn't quite a heavy as lead, but if we calculate the buoyant weight we see they are pretty similar.
For 1 pound of lead (specific gravity 11.34):

• In fresh water: 0.912 lbs
• In salt water: 0.910 lbs

For 1 pound of cupronickel (specific gravity 8.95):

• In fresh water: 0.888 lbs
• In salt water: 0.885 lbs

As far as volume, if we wanted 1 lb of buoyant weight in salt water we would need

• 1.5 in^3 of lead
• 2.0 in^3 of cupronickel

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Q:There is no way I'm fitting 1000 nickels into my BCD, how could that ever work?

Have you tried? Soft pouches of nickels are not much bigger than soft pouches of lead. This is in part because coins are bigger disks than shot (the geometry means better space filling), and in part because the density is still high. If you can fit 11 pounds of lead shot sacks, you can fit 1000 nickels (11 lbs).

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Q: How much does cupronickel cost vs lead?

In some sense cupronickel is free. If I "buy" 4 lbs of nickels it means I need 363 nickels at $18.15. But using those nickels does not impact their value so I can spend them again later. They retain 100% of their value.

In contrast a 4 lb lead weight may cost ~$20, is toxic, and has little to no resale value (maybe even a toxic waste handling fee).

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Q: I've seen copper corrode, but not lead, so does this mean that lead is more stable in water?

Unfortunately not. The difference is that lead corrosion is white or clear, so doesn't make as much of a visual impact. But just because we don't see it clearly doesn't mean it isn't happening. Look at an old dive weight and you will see ample evidence of corrosion.

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Q: Isn't copper toxic to aquatic life?

Yes, copper ions are toxic. Actually nickel ions are even more toxic, but neither is as toxic as lead. As a case in point, consider the WHO drinking water standards:

• Lead: <10 µg/L, with goal of 0.
• Nickel: < 70 µg/L
• Copper: <2000µg/L

This coupled means that a lead weight is much more potent of a negative impact.

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Q: I've been using lead for years, and I'm fine, why should I care?

Lead exposure is a slow and progressive issue. There is no positive effect of lead ingestion and a huge literature of negative impacts from neurological, cognitive, and reproductive harm. Kind of like smoking and asbestos--we know those are harmful but they are not a death warrant. The question is if we have viable alternatives, and we do.

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Q: I only dive a few times a year and I just rent my weights, so why should I care?

Lower lead use does lead to lower exposure, that is true. But you are still exposing yourself, your suit, and your equipment to lead which will come home with you. Also the dive operator who handles the weight every day has a much higher exposure rate.

Furthermore, the whole point of a dive is to drop the weight if you are in an emergency. If you drop a dive weight you are creating a point source of lead contamination in, most often, a fragile reef ecology.

Choosing lead not only impacts you.

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Q: I've heard that coins kill fish, that is why we don't throw pennies into wishing wells. Won't wearing coins kill fish?

That depends the coin, and a wishing well with fish has recirculated water that magnifies any contamination. Lead is more toxic to fish than nickel or copper. Cupronickel corrodes very slowly in water, while lead is faster. Given that, shifting to cupronickel (nickel coins), would be a more fish friendly option.

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Q: Plastic coated lead weights are fine as they contain the lead, so why not just use those?

Plastic coated lead still has problems. The plastic coat often has a vent hole, or even if not, the coat will, with time, develop cracks. Those holes and cracks will allow water intrusion behind the plastic against the lead. This water can't be rinsed off easily so will stand on the weight for much longer than an uncoated weight. This means more time for the metal to corrode. That corrosion will then leach out on the next dive.

Also the lifecycle problems of lead are not removed by coating it in plastic. In some cases, it makes the lifecycle harder in that many recyclers will not take a plastic coated weight because it is a mixed waste.

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Q: I don't live or dive in the US, so are there other coins I can use?

Yes! Many countries have cupronickel coins (see the coin calculator for different currencies). Fortunately, many more tropical countries use cupronickel as coinage expressly because it is resistant to corrosion and salt spray.

Other coins like the Australian dollar and two dollar coins work well too (aluminum bronze). Avoid coins that are bi-metallic and/or contain zinc or steel--those will corrode more quickly than we would like.

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Q: Nah, why bother with all of this when I can just dive and recover old fishing lures, wheel weights, and junked lead belt weights, melt them down and make shiny new free lead weights?

This is a bad idea. Lead in the environment is bad, but smelting your own lead is a really bad idea. When you melt lead, you can easily expose yourself, family, and environment to really toxic lead fumes. That and you are making your space into a superfund site.

Instead, go to the bank and get a bag of nickels instead.

 

[tursiops]

Welcome to ScubaBoard. Interesting first post. Well-written, somewhat compelling.
Your personal website is also interesting, Have you ever actually sold any SS weights at $240 for 3 lbs?

Question about lead being toxic. Yes, of course. But in the context of the ocean as a dilutant, does it really matter what metal divers use? Are not plastics a bigger problem in the long run?

 

[Landau]

Very interesting, I immediately tried looking up my local currency but your calculator doesn’t include Canada.

 

[Tanks A Lot]

I truly applaud your goal of getting rid of lead in the diving industry. It has long been a bother to me how nonchalant the SCUBA industry is about the issue when lead poisoning has been a known problem for decades, or better said nearly a century now. I believe the trouble is that lead poisoning is such a slow process, usually taking decades for adults. The trouble is that it is an accumulative process, in contrast with many other poisons.

However, I have a small nitpick with your data, as I believe looking at the facts objectively is always important. The corrosion rate of lead should be far slower than the data you quoted of 2.8–15.2 mm/year. I'd be interested to know where you got this data from. Lead and many of its alloys have the peculiar habit of forming a protective passivation layer in the presence of salts. This layer slows down the corrosion of the base alloy considerably.

Also, the alloy initially forms Leadoxide (PbO), which can react with CO2 from the environment to form Pb₅O(OH)(CO₃)₂, which is called plumbonacrite, which makes the passivation layer very resistant to corrosion. There are a few other reactions taking place, especially with Chlorides, but the end-result is, that the forming patina is very stable.

Some of the sources you cite, for example the ASM Handbook, acknowledge this. It gives a corrosion rate of 1 µm to 1.3 µm per year in a marine environment. This would amount to 0.001 mm to 0.0013 mm per year of corrosion. This is also more in line with what most people will know from personal experience.

ASM Handbook, Volume 13B: Corrosion: Materials

However, the protective films that form on lead and its alloys are so effective that corrosion is insignificant in most natural atmospheres. The extent of this protection is demonstrated by the survival of lead roofing and auxiliary products after hundreds of years of atmospheric exposure. In fact, the metal is preserved permanently if these films are not damaged (Ref 10).

Lead can corrode rapidly under certain conditions, but these usually involve CO2, chlorides, or some other strong oxidizing agents in high concentrations.

That being said, I believe this by no means diminishes your goal of getting rid of lead in the diving industry. I hope that people follow suit and that alternatives will become more widely available to the broader masses and dive shops.
The toxicity of lead and especially of melting it can not be overstated! Especially in poorer countries this is done with zero protection, sometimes even in enclosed spaces.

 

[pwoolf]

Welcome to ScubaBoard. Interesting first post. Well-written, somewhat compelling.
Your personal website is also interesting, Have you ever actually sold any SS weights at $240 for 3 lbs?

Question about lead being toxic. Yes, of course. But in the context of the ocean as a dilutant, does it really matter what metal divers use? Are not plastics a bigger problem in the long run?

Thanks! I've sold a few of my own stainless weights yes ($250 for 6 lbs), but while those are really nice, they are not cost effective for most divers. I get that.

As for lead in oceans, you are part correct. As my chemical engineering colleagues say "the solution to pollution is dilution".

But there are three areas where this impact is concentrated:

1) Human dive operators: These are the people that handle the weights most often and live around them. Their occupational exposure is high, and that doesn't have to be.

2) Divers: The diver, when they do handle the weights, are exposing themselves to lead. This exposure is generally not high and not often, but no amount of lead exposure is good.

3) Point source environmental: If a lead weight is dropped, then it creates a lead rich microenvironment. While the sea is vast, the coral and fish surrounding the dropped and corroding lead weight will experience much higher levels of lead.

As for plastics, yes. Both/and. We have many ways we are impacting our waters. The lead weight problem is one just happens to be one that is incredibly easy to fix with cupronickel.

 

[pwoolf]

Very interesting, I immediately tried looking up my local currency but your calculator doesn’t include Canada.

Ha, yes. Unfortunately I could not find any Canadian coins that are cupronickel. They tend to be most popular in tropical countries for the same corrosion reasons that I like them (resistant to salt spray and humidity),

If you know of a Canadian coin that is cupronickel let me know and I will add it!

 

[pwoolf]

However, I have a small nitpick with your data, as I believe looking at the facts objectively is always important. The corrosion rate of lead should be far slower than the data you quoted of 2.8–15.2 mm/year. I'd be interested to know where you got this data from. Lead and many of its alloys have the peculiar habit of forming a protective passivation layer in the presence of salts. This layer slows down the corrosion of the base alloy considerably.

Also, the alloy initially forms Leadoxide (PbO), which can react with CO2 from the environment to form Pb₅O(OH)(CO₃)₂, which is called plumbonacrite, which makes the passivation layer very resistant to corrosion.

Some of the sources you cite, for example the ASM Handbook, acknowledge this. It gives a corrosion rate of 1 µm to 1.3 µm per year in a marine environment. This would amount to 0.001 mm to 0.0013 mm per year of corrosion. This is also more in line with what most people will know from personal experience.

ASM Handbook, Volume 13B: Corrosion: Materials


Lead can corrode rapidly under certain conditions, but these usually involve CO2, chlorides, or some other strong oxidizing agents.

Yes, finding good data on lead corrosion (and corrosion in general) is tough. The corrosion rate I took from that ASM handbook, Table 2. I chose table 2 because it was not in lab conditions but instead in natural conditions. They range between 2.03 - 12.7 um/year (12.7 is for Bristol Channel exposed to sea water approximately 93% of the time, based on the notes in the table).

The mechanical action and biological action of corrosion play a role. I could see a dive weight actually corroding faster than this because it is mechanically scraped by the dive suit and handling (lead chloride and lead carbonate don't make a very strong surface layer). But I didn't have data for that so I took the closest marine data I could find.

EDIT: Ah, I see I screwed up some of my units! Good catch! Thank you!

 

[Tanks A Lot]

Ah, I see where our discrepancy comes from. The table you quote is in micrometers (µm) not millimeters (mm), which makes the earlier quoted data off by a factor of 1000.

 

[pwoolf]

Ah, I see where our discrepancy comes from. The table you quote is in micrometers (µm) not millimeters (mm), which makes the earlier quoted data off by a factor of 1000.
View attachment 872892

Yes, which is kind of interesting. I've got in my notes that a corrosion rate of for lead at 0.13 mm/year and recall reading that somewhere. Now I'm trying to track that down!

If we take it at these ranges from Table 2 (0.002 to 0.013 mm/year) then they are around that of 316 stainless steel, which doesn't seem correct to me.

EDIT: Looking further I do find data on lead corrosion, interestingly it comes from the nuclear reactor industry.

https://inis.iaea.org/collection/NCLCollectionStore/_Public/31/060/31060544.pdf?r=1

They list a corrosion rate of 0.001 mm/year for "neutral carbonated ground water" but for salt water or distilled water they find 0.56 mm/year.

 

[lexvil]

Why not just make weights from Monel?