Toxic Darkroom Effluent
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Lloyd Erlick.
July 3, 1998

Many discussions of the toxic substances we release from our darkrooms center on 'fixer' and 'selenium toner.' I would like to present my viewpoint on these substances, as well as a few more appearing briefly at the end of this article.

In actual reality, fixer itself is quite harmless, especially the 'plain fix' I describe elsewhere on this website. It contains only two components, besides water: sodium thiosulfate and sodium sulfite. Both of these substances are relatively innocuous, and are used in industries other than photography. In fact, if the entire photo industry gave up these substances, mountainous quantities would still be used. We darkroom folks have cheap supplies of these substances because they are used elsewhere in such large amounts. Boatloads and trainloads of them arrive in most populous places quite frequently and regularly, enabling us to visit the warehouses and buy single bags (50 to 100 pound bags!) at reasonable cost. Sodium sulfite is used in the food processing industry in huge quantities, and a large fraction of these quantities are processed through human digestive tracts before disposal.

Of course, it is spent fixer that is the problem. This is fixer that has had numerous sheets of photographic paper, or numerous films, processed through it.

As we all know, the purpose of fixer is to remove the parts of the photosensitive coating of film or paper that is non-image. In other words, the parts of the photosensitive layer that have received no exposure. Of course, these parts of the photosensitive layer contain silver compounds. It is the compounds of silver that make it photosensitive.

The problem with darkroom fixer effluent is that it contains silver, often referred to as 'silver complexes.'

The longer and/or more frequently a fixing bath is used, the closer it comes to its exhaustion point. This is where it will no longer remove silver compounds from the photosensitive layer. Beginning with the first sheet of paper or roll of film, silver in the fixing bath is entering into chemical reactions within the fixing bath. The reaction products containing the silver (the silver complexes) become more and more 'complex', meaning they are larger and larger molecules, as the fixing bath proceeds through its working life and approaches exhaustion. At exhaustion, the silver complexes are at their most 'complex' point.

The significance for darkroom workers is that these complexes find their way into the fibers of our paper. The same is true for film and RC paper, but penetration is of the photosensitive layers, not the support base. These complexes are relatively insoluble, and the difficulty of removing them from paper fibers increases as their complexity increases.

In other words, the silver effluent of a fixing bath near its exhaustion point is worse than the silver complexes formed relatively close to the beginning of the fixing bath's life. From the standpoint of washing the photosensitive material (I'll discuss it from the perspective of FB paper, which is the most difficult case), the silver-bearing products of a relatively fresh fixing bath are easier to remove than those of a much-used bath.

The implications for darkroom workers concerned with the substances they are releasing into the environment are clear.

Since the worst of the silver complexes form late in the life of a fixing bath, we can avoid them entirely by using our fixer only part way to exhaustion. This pays off for us in two ways:
  1. We must deal only with the silver complexes that are relatively easy to wash out of paper fibers.
  2. We need not dump the worst silver compounds into the environment. In other words, we minimize the environmental impact of our darkroom activity in this area.
The useful-capacity rating for the type of fixer I use is usually given as 25 8x10s per liter, or an equivalent surface area of other sizes. I usually think of this as 75 8x10s for my fixing bath, because I almost always mix up 3 liters at a time.

Most of the time I stop using my 3 liter fixing bath after I've put 40 to 50 8x10 equivalents through it. Most of my work is on 16x20 size sheets of FB paper, so I think of the fixing bath as finished after I've processed 10 to 12 sheets of paper. At my rate of production, this is about two working sessions.

These days (July 3, 1998 ) my 16x20 material is costing me just over C$3.00 per sheet. The above rationale implies ten to twelve times three dollars per sheet, or 30 to 36 dollars worth of paper per 3 liter mix of fixer. The fixer I use costs me a good deal less than one dollar per liter, which translates to much less than the cost of one sheet of paper for my 3 liter fixing bath.

This is cheap enough for me. I feel no need to squeeze out any more pennies. Doing so would only get me into a more difficult situation as regards washing the sheets of paper, and force me to release worse silver-bearing substances. It is possible that the added difficulty of washing would necessitate enough added expenditure on water and energy to warm the water that it would negate the savings from using the fixer to a higher degree.

Additionally, it is not strictly necessary to release ("dump") the spent fix. Small scale silver recovery units exist, although their efficacy for small scale darkrooms is open to question. In many places there are respectable photographic suppliers and camera stores that operate silver recovery units on a larger scale than the individual worker. They will often take spent fixer and put it through their system. In Toronto, there is West Camera in the downtown area. They not only take spent fixer, but pay one dollar for a gallon! Very likely many other honorable photographic specialty shops exist all over North America and elsewhere.

Because 'plain fix' is so cheap and easy to prepare, sometimes it might be feasible to use it only once, perhaps even for only one sheet. If I were asked to produce a 16x20 or 20x24 print for a substantial amount of money, or even better, several such prints for enough money per print, I might mix a batch of fixer for each print. There is no need to feel bad about the excess sulfite and thiosulfate being used, and the silver effluent resulting would be small in each bath. The resulting prints would be easy to wash, since they would have only the minimal silver complex content trapped in their fibers. There would be a certain amount of work involved preparing the fixing baths, but of course this fantasy includes high pay per print to justify it!

The problem of fixer effluent should be viewed as a problem of the amount of silver-bearing photosensitive material we use. Fixer itself plays little or no role.

Selenium toner is another source of toxic material for us to release.

Selenium itself is not particularly toxic, although buying pure selenium powder and proceeding to mix up toner is ill-advised. Like anything in finely divided form, it is easily carried into the lungs. Bakery workers would understand this problem immediately, even though flour is not outright toxic. Handling any powder properly to avoid breathing the dust requires proper knowledge and equipment, even for darkroom commonplaces like D76 or Kodak Fixer. I would advocate that no one handle selenium powder in their own darkroom or home for any reason.

The problem with selenium is that it reacts with other substances to form soluble reaction products which are toxic. When it reacts to form insoluble reaction products, they tend to be less toxic. A good example is silver selenide, which is formed on a photographic print as it is being toned. The color we see in a selenium toned print is the color of silver-selenide coating the microscopic particles of silver metal we have in our print. It's very fortunate that humans find this color agreeable, because this selenide coating (or plating) on the silver particles also protects the silver from many substances that would react with it and degrade the image. Sulfur dioxide, a common air pollutant, is a good example.

Unfortunately, when we buy a bottle of selenium toner concentrate, we are buying a soluble form of selenium. So the bottles of selenium toner we have on hand contain a toxic substance, although not a hugely toxic nor highly concentrated one. It does not travel through the air to poison us, although the powerful odor of ammonia could make us believe it does. That odor comes from the ammonium thiosulfate which comprises a large part of the selenium toner concentrate. (Examine the ingredients listed on the label of Kodak Rapid Selenium Toner.) Ammonia is a dangerous substance in itself, although it is also a very common household chemical. Ventilation is advised to get rid of ammonia if we are going to be closeted with it in the darkroom.

Selenium itself, in its soluble compound form in selenium toner, does not travel through the air (unless we are spraying a mist of the stuff around the darkroom!) To avoid getting it in the body, avoid drinking it and avoid contact with the bare skin. If a splash occurs and it gets on bare skin, there is no need to fear. Washing it off immediately with soap and large amounts of water suffices. Ansel Adams is reputed to have exposed his hands to selenium toner, as well as every other darkroom substance. I would very much like to have corroboration for the intriguing darkroom myth that he left instructions for his body tissues to be analyzed after his death to provide information as to the results of his chemical exposures.

To put it in perspective, cleaning a cat litter box might expose us to more ammonia than a tray of selenium toner. If the cat box is left too long between cleanings, the biodegradation of the cat urine in the box will release a good deal of ammonia. It is not necessary to fear a cat box or a tray of selenium toner. Proper measures are easy to take: clean the box regularly and ventilate the darkroom.

As to the selenium in soluble-compound form in the toner solution, the proper place for it is on the prints. Using the selenium toner causes the selenium to reside on the print, which is where we want it. Using a selenium toner bath to exhaustion puts the selenium on the prints and minimizes what we dump.

Of course, this is simplistic. We can not reduce the selenium effluent from the darkroom to zero this way. But we can do our best, and in the process we get the benefit of the toner on our prints.

When we do dump a bath of selenium toner, it goes to one of several places: a municipal water treatment facility (as in my case, because I live in a large city and in a district zoned for the type of activity in which I engage), or a septic tank.

Both of these receptacles for waste selenium toner ultimately cause the selenium to react to form insoluble products, which are the least toxic forms for selenium. The septic tank will do it by biological activity. The same will occur over a long period of time if the toner is dumped on the ground and abandoned (this is strictly figurative! Do not do this!)

Obviously, care must be taken with regard to the final destination of the waste selenium toner, because a septic tank too close to a well or water table or underground water course will permit toxic soluble selenium compounds to reach them long before the insoluble compounds are formed. But a septic tank too close to a well or water table is a horror show for much more pressing reasons than a bit of darkroom effluent. Human fecal waste comes to mind in this regard.

In days gone by, potassium cyanide had a place in the darkroom. Mercury compounds still have applications, but not in ordinary darkrooms. Most darkroom workers should shun anything with mercury in it - including thermometers! Anyone with a mercury thermometer in the darkroom would be well advised to know and be equipped to carry out the protocol for capturing and disposing of all the mercury released from a broken thermometer. It is much easier to do without this type of thermometer.

Potassium ferricyanide is commonly used today for bleaching prints, but its toxicity is quite low compared to other cyanide compounds. It is often sold in one pound containers, very likely a two-lifetime supply for most darkroom folks. The amount used at one session is quite small, and disposal with copious amounts of water dilutes it sufficiently for some measure of safety.

Thus the worst waste products of the average darkroom are not particularly bad, and can be disposed of in their least-bad forms. Many other toxic substances can be used in the darkroom, but need not be used frequently or at all.

Copyright Lloyd Erlick. All rights reserved.