Barnes Bullets

Tungsten Facts

Tungsten Leaching into Waterways
Vic Oltrogge
May 2007

The fact that several versions of “tungsten leaching into water supplies in New England” are being heard has prompted this clarification of a few relevant points.

Elemental (pure, metallic) tungsten is not water leachable.

Tungsten is a heavy metal in Group VIB of the Periodic Table, exhibiting very high density and melting point, and is often called a refractory metal. It is capable of forming a wide variety of compounds, and confusion of elemental tungsten (symbol W) with tungsten compounds is the source of much disinformation regarding the “toxicity of tungsten.” That confusion also creates misunderstanding of the transportability of elemental tungsten vs. compounds of tungsten by unintended means.

There are quite a few compounds of tungsten that show noticeable toxicity, including but not limited to oxides, borides, nitrides and silicides. They tend to be divided into soluble and insoluble compounds, especially in the toxicity literature (ref. 2), but for present purposes they need not be distinguished.

It is highly significant that with but one exception, none of the studies referenced below mentions the toxicity of elemental tungsten. The exception is ref. 6 at page 259 where the LD50 of elemental tungsten is given for reference. It differs dramatically from the values for the listed tungsten compounds, being on the order of 10,000 times greater. The other references obviously consider the toxicity of elemental tungsten unworthy of comment under the tungsten toxicity topic. But this point requires considered review.

Frequently the references mention “the toxicity of tungsten” at a stated concentration without explicitly noting that they are referring to a tungsten compound and not to elemental tungsten. The listed concentrations present correct values for the amount or percentage of tungsten atoms in the subject compound, (or compound with additional carrier), but do not imply presence of any elemental tungsten. Note especially ref. 6, page 258, “With diets containing 0.5% W, both tungstic oxide and simple tungstate salts are toxic, while ammonium paratungstate is not.” The 0.5 % W is not a percentage of elemental tungsten found in a particular diet. It is the percentage of tungsten, existing as atoms tied up in tungsten compounds, expressed as a percentage of the total weight of subject diet. Similarly a water sample could be reported as containing “0.5 % W” but it is important to observe that such reports refer to tungsten that is tied up in tungsten compound(s) existing in the water. As with the diet, the percentage figure is the percentage by weight that tungsten atoms form of the total water sample, which tungsten atoms are tied up in tungsten compounds. It is because the tungsten atoms are part of a tungsten compound(s) that there may be significant toxicity. Note above that the tungsten compound ammonium paratungstate is not toxic.

The references go into detail on the toxicity of elemental nickel, chromium and zinc, as well as the usual list of toxic metals such as arsenic, lead, mercury, selenium, thallium and the like. The toxicities of compounds of tungsten are treated in similar detail, reporting significant toxicity for many of them. But the references do not make any mention of the toxicity of elemental tungsten, with the exception of ref. 6 as mentioned above, showing that the toxicity of elemental tungsten is vanishingly small.

There are several aspects to the discovery of tungsten in water supplies. An important one has to do with the analytical methods of detecting the tungsten. The analytical processes break down the tungsten compound, or the tungsten alloy (see below), so that the tungsten content can be measured. Those methods report the relative concentrations of all the types of atoms that are found in the tested sample. When tungsten is included in the typically long list of atoms reported, it requires singular expertise in dealing with the compounds of tungsten to deduce which compounds were probably involved in carrying the tungsten. Determining the particular tungsten compound(s) is a complex analytical challenge, and is a procedure that is seldom done. Lack of acquaintance with tungsten chemistry can easily result in an erroneous conclusion that elemental tungsten has leached into the water. Elemental tungsten is not soluble in water.

Leaching is the process of removing soluble constituents from a substance (such as top soil or substrates in this case) by the percolating action of a liquid. Tungsten cannot be leached into a water supply by the movement of the water because of the insolubility of elemental tungsten in water. Elemental tungsten is insoluble in nearly all known liquids. To dissolve elemental tungsten or tungsten alloys requires a rather vicious mixture of nitric acid and hydrofluoric acid. Whether for purpose of chemical milling or dissolution for analytical process, the HNO3 - HF mixture is used.

If tungsten is found in water, it is almost certain that it is present as a compound of tungsten. On the other hand, if elemental tungsten is found in the water, its presence is of no concern due to its negligible toxicity. In addition, tungsten is so dense, nineteen times as dense as water, that it is exceedingly difficult for water to carry it. Average rocks are only about three times as dense as water. Elemental tungsten cannot be converted to a compound of tungsten by reaction with the water as tungsten is inert in water. The presence of tungsten compounds in waterways is likely the result of present or past processing of tungsten at an upstream location which releases those compounds, or through the intentional use of tungsten compounds somewhere upstream. Tungsten compounds are used to waterproof papers and textiles, so detection of tungsten should trigger search for a history of upstream facilities of those sorts. Tungsten ores contain compounds of tungsten, but mining does not usually free them. Processing of the ores frees the compounds and breaks them down via chemical means. The reverse of that process, the combining of elemental tungsten into compounds, also requires complex chemical means. Tungsten mining and the processing of tungsten ores occur in only a few locations worldwide.

Metal alloys that contain tungsten are not a source of tungsten compounds. Metals are crystalline, meaning that the atoms thereof are arranged in definite, repetitive, three-dimensional patterns. In alloys, the atoms of the alloying element either replace atoms of the solvent metal in its crystal lattice (substitutional alloying) or they squeeze into spaces between the solvent atoms (interstitial alloying). They do not form chemical compounds in the sense of anionic/cationic valence arrangements referred to above as compounds of tungsten. In metallurgical usage, alloys that are called “intermetallic compounds” occur in specific atomic ratios but are not valence bonded. Thermodynamic matters determine the atomic ratios, and simple melting can alter the structure. Therefore alloys such as the common tungsten-copper-nickel alloys that are used to replace lead for X-ray shielding are not compounds in the chemical, toxicological sense. They are not the “compounds” treated in the references.

At one time it was thought that tungsten in the cemented carbides used for cutting tools, as in machine shops, was the source of observed toxicity derived from breathing dust during the grinding of such tools. It has since been found that the toxicity derives only from the cobalt and/or nickel that is included in the cutting tool – not the tungsten. Therefore the exposure limits for such dusts are now based on the content of those two elements: cobalt at greater than 2% or nickel at greater than 0.3% trigger the hazardous material warning (ref. 2.). This is not a matter of compounds of tungsten, but of the creation of sufficiently small particles of the alloy to allow the cobalt and/or nickel to be biologically accessible. Again the negligible toxicity of elemental tungsten is confirmed.

Not only, then, is the leaching of elemental tungsten into waterways a highly unlikely event, it would also be an event of no consequence. Tungsten compounds of the valence-based type are another matter, but they cannot be created by immersing elemental tungsten in water, due to the inertness of that combination. Other sources are responsible.

Silvex® is the core material of the Barnes MRX bullet. It contains no chemical compounds of any kind, much less a compound of tungsten. Neither does it include an intermetallic compound of tungsten, though such would be insignificant toxicologically. Other metals are included in Silvex® but they too are nontoxic. Further, they are not capable of catalyzing the conversion of elemental tungsten into a compound of tungsten. Silvex® is nontoxic per the US Fish and Wildlife Service, having passed without reservation the specified test program using live ducks in test and control groups. Google US Fish and Wildlife, toxicity, Federal Register for details. The Colorado State University School of Veterinary Medicine performed additional tests of their own creation, involving implantation of Silvex® into muscle tissue. No toxicity was discovered.

In summary:

•Elemental tungsten demonstrates no toxicity.
•Some compounds of tungsten are toxic.
•Elemental tungsten is not leachable by water
•Elemental tungsten cannot be changed into compounds of tungsten short of laboratory methods.
•Typical analysis for tungsten does not distinguish between elemental tungsten and tungsten compounds.
•Reports of tungsten in water beg detection of the tungsten compounds that were present.
•Silvex® contains no tungsten compounds, or other toxic material, nor potential for their creation.
•Silvex® is nontoxic per the mandated US Fish and Wildlife tests, and also per additional tests performed by the Colorado State University.

References

1. Toxicity of Heavy Metals in the Environment
Ed. F. W. Oehme Marcel Dekker NY 1978

2. Hazardous and Toxic Effects of Industrial Chemicals
Marshall Sittig Noyes Data Corp. Park Ridge NJ 1978

3. Environmental Hazards of Metals
Brakhnova & Slep Consultants Bureau NY 1975

4. Effects and Dose-Response Relationships of Toxic Metals
Elsevier Scientific Publications Co. NY 1976

5. Metal Toxicity in Mammals I
Luckey and Venugopal Plenum Press NY 1977

6. Metal Toxicity in Mammals II
Luckey and Venugopal Plenum Press NY 1977

*Permission is hereby granted to copy/quote this paper in its entirety only. Permission to copy/quote in part is not granted.