Silver's Shadow: The Real Environmental Crisis in Your Darkroom

Part 2 of 13 in the Sustainable Darkroom series | ← Previous: Part 1 | Next: Part 3 →

The previous post in this series examined botanical developers—caffenol, wine, tea, juniper—and what they actually offer environmentally. The conclusion was measured: real but limited advantages, primarily around disposal toxicity, with poorly quantified lifecycle trade-offs.

But writing that post unsettled something. I kept returning to a nagging thought: if I'm worried about the environmental impact of developer, what about fixer? Developer reduces silver to form the image. Fixer dissolves the unexposed silver so it doesn't darken in light. That dissolved silver has to go somewhere.

I did the calculations. What I found reframed everything. The caffenol-versus-Rodinal debate suddenly seemed absurd—an argument about furniture arrangement while the house is flooding.

This post is about fixer: what it contains, why it matters, and why developer choice is nearly irrelevant compared to what you do with your spent fixer.

The Chemistry of Fixing: Where Silver Goes

Let me start with the mechanics, because understanding them clarifies why fixer is uniquely problematic.

When you expose film, light converts a tiny number of silver halide crystals into development centres—metallic silver atoms that catalyse further reduction during development. But only a fraction of the emulsion's silver halides are affected. The vast majority remain unexposed, undeveloped, and still light-sensitive.¹

The fixer's job is to remove these unexposed silver halides so your negative can safely exist in daylight. Thiosulfate ions (from sodium or ammonium thiosulfate) form soluble complexes with silver:

AgBr + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Br⁻

The silver doesn't vanish. It dissolves into your fixer as silver thiosulfate complexes, accumulating with every roll you process.²

A typical roll of 35mm film contains roughly 50–100 milligrams of silver in its emulsion.³ When you fix that roll, most of that silver ends up in your fixer. If you're processing 10 rolls per litre of working fixer (a conservative estimate), you're accumulating 500–1,000 mg of silver per litre before the fixer exhausts.

Commercial photofinishing labs, running fixer continuously, routinely reach 5,000–12,000 mg/L of dissolved silver.⁴ Even home darkroom practitioners typically hit 3,000–8,000 mg/L before fixer performance degrades noticeably.

To put this in perspective: you're working with a solution containing 3–12 grams of silver per litre. That's not a trace contaminant. That's substantial dissolved heavy metal.

Silver Toxicity: The Numbers That Should Alarm You

Now consider what happens when silver enters aquatic environments.

I'm not an ecotoxicologist. But I can read a table, and I can do the maths. When I started looking into this, I expected silver to be mildly problematic—a heavy metal, sure, but probably requiring significant concentrations to cause harm. I was wrong by several orders of magnitude.

The standard measure for aquatic toxicity is the LC₅₀: the concentration that kills 50% of test organisms over a defined period. I found these values in EPA documents and peer-reviewed ecotoxicology papers.⁵ The numbers for silver are remarkably low:

• Daphnia magna (water flea): 0.6–0.66 μg/L kills half the population in 48 hours
• Rainbow trout: 5–6.5 μg/L over 96 hours

Note the units: micrograms per litre. Parts per billion. These tiny crustaceans—which form the base of many freshwater food webs—die at concentrations below 1 μg/L.

Your spent fixer contains silver at 3,000,000–8,000,000 μg/L.

This is where my physics training kicks in: when you see a ratio like that, you pay attention. Spent fixer contains silver at concentrations roughly ten million times higher than lethal thresholds for sensitive aquatic species.

Now, I don't know exactly how these laboratory values translate to real watersheds. Dilution matters. Binding to sediments matters. Municipal treatment removes some fraction. But even if you dilute spent fixer by a factor of 10,000—which is a lot of dilution—you're still at concentrations 1,000 times higher than what kills invertebrates in controlled studies.

The US EPA's RCRA hazardous waste threshold for silver is 5 mg/L (40 CFR § 261.24)—a regulatory line that bears no obvious relationship to the ecological data.⁶ Meeting that threshold still produces effluent 5,000–10,000 times more concentrated than laboratory LC₅₀ values. Spent fixer exceeds even this permissive threshold by 600–1,600×.

The Developer Comparison: Quantifying Irrelevance

Let me now compare fixer's silver content to the chemicals we actually argue about.

The previous post examined hydroquinone—the most toxic common developing agent. Its aquatic toxicity values from ECHA registration dossiers:⁷

• Fish LC₅₀ (96h): 0.044–0.638 mg/L
• Daphnia magna EC₅₀ (48h): 0.061–0.142 mg/L

These are concerning numbers. Hydroquinone is genuinely harmful to aquatic life, classified as Aquatic Acute 1 and Aquatic Chronic 1 under CLP. The concerns about it aren't manufactured.

But let's compare actual concentrations in photographic waste:

Solution	Primary Toxicant	Concentration	Most Sensitive LC₅₀
D-76 developer	Hydroquinone	~2,000 mg/L	0.044 mg/L (fish)
Spent fixer	Silver	~5,000,000 μg/L	0.6 μg/L (Daphnia)

The ratios tell the story:

• D-76 contains hydroquinone at approximately 45,000× its LC₅₀
• Spent fixer contains silver at approximately 8,000,000× its LC₅₀

Fixer's silver is roughly 180 times more hazardous relative to toxicity thresholds than developer's hydroquinone—and that's comparing the most toxic conventional developer to a heavy metal. If you're using ascorbic acid-based developers (Xtol, Eco-Pro) or caffenol, the developer's toxicity contribution becomes vanishingly small, while fixer's remains constant.

There's another crucial difference: biodegradability.

Hydroquinone is readily biodegradable. OECD 301C testing shows 70% degradation within 14 days, meeting the “window criterion” for ready biodegradability.⁸ Activated sludge treatment removes >99.9% of hydroquinone from wastewater.⁷ Surface water half-life is approximately 20 hours. The compound is problematic, but environmental persistence is not among its problems.

Silver isn't biodegradable. It's an element. It doesn't break down. Wastewater treatment plants can remove silver from the water column—greater than 90% partitions to sludge⁹—but this merely transfers the metal to biosolids, which are then land-applied or landfilled. The silver remains in the environment indefinitely, potentially bioaccumulating through food chains.

When you pour spent fixer down the drain, you're not releasing a compound that will eventually decompose. You're introducing a persistent heavy metal into whatever ecosystem your wastewater eventually reaches.

The Fixer Hierarchy in Photographic Waste

This isn't just my analysis. Industry data confirms fixer's dominant role in photographic environmental impact.

Kodak Publication H24.06, the most comprehensive effluent characterisation for photographic processing, provides comparative data for motion picture processing:¹⁰

Process	BOD₅ (mg/L)	Silver (mg/L)
D-96 B&W Negative	14,000	3,000–5,000
D-97 B&W Print	5,600	2,000–4,000
ECN-2 Colour Negative	1,300–1,700	500–1,500

Where Kodak specifically notes that fixer may contribute more than half of biochemical oxygen demand BOD₅ in black-and-white processing waste. The BOD₅ values of 5,600–14,000 mg of oxygen consumed per litre represent 5–50 times stronger waste than typical municipal sewage (200–300 mg/L). Processing chemistry places genuine stress on treatment systems.

But the silver content is what triggers regulatory classification. Under US RCRA regulations, any waste containing ≥5 mg/L silver is classified as hazardous waste (D011).⁶ Virtually all spent fixer exceeds this threshold by 600–2,400×. The developer, whatever its chemical composition, rarely triggers hazardous waste classification.

The EPA's 1997 Preliminary Data Summary of the Photoprocessing Industry concluded that at municipal sewage dilution ratios, most photographic effluent constituents (thiosulfate, sulfite, ammonia-nitrogen) are of “insignificant environmental consequence” and amenable to biological treatment.¹¹ The exception was silver, which required pre-treatment or source reduction.

Nearly thirty years later, this assessment remains accurate. The organic chemistry of photographic processing is manageable. The silver isn't.

Is There a “Green Fixer”?

Given all this, a reasonable question: can we fix the fixer? If botanical developers offer lower-toxicity alternatives to hydroquinone, perhaps there's an equivalent for thiosulfate?

I looked into this hoping to find something. The answer is instructive.

How fixer is made: Sodium thiosulfate—the active ingredient in standard fixer—is produced industrially by reacting sodium sulfite with elemental sulfur: Na₂SO₃ + S → Na₂S₂O₃. It's straightforward inorganic chemistry, relatively low-energy, no exotic feedstocks. Ammonium thiosulfate (rapid fixer) is similar. Neither production process is notably dirty by industrial chemistry standards.

Is thiosulfate itself toxic? No. Sodium thiosulfate is used medically to treat cyanide poisoning. Aquarists add it to dechlorinate tap water for fish tanks. It's biodegradable—wastewater bacteria break it down readily. The EPA assessment I cited earlier explicitly notes that thiosulfate is of “insignificant environmental consequence.” If spent fixer contained only thiosulfate, you could pour it down the drain without concern.

What about alternatives to thiosulfate? They exist, but they're worse:

• Cyanide-based fixers were used in the 19th century. Extremely toxic. No one wants to go back.
• Thiocyanate fixers work but are more toxic than thiosulfate and slower.
• Thiourea-based fixers have been researched but offer no environmental advantage and introduce their own toxicity concerns.

Thiosulfate became the standard because it's effective, cheap, relatively safe, and biodegradable. There's no botanical alternative waiting to be discovered. The chemistry is already about as benign as fixing chemistry can be.

The uncomfortable conclusion: The fixer isn't the problem. The silver in the fixer is the problem. And you can't avoid the silver, because removing unexposed silver halides is the entire point of fixing. Every frame you shoot deposits silver into your fixer. That's not a bug in the process—it's the process working correctly.

There's no formulation change, no alternative chemistry, no eco-friendly product that eliminates this. The only intervention that matters is what you do with the silver after it accumulates: recover it, or dispose of the fixer properly, or release it into the environment. Those are the options.

What This Means for Sustainability Practice

If you genuinely care about minimising your darkroom's environmental impact, the hierarchy is clear:

1. Silver management (non-negotiable) Whatever developer you choose—caffenol, Rodinal, D-76, Xtol—you must address the silver in your fixer. Without silver recovery, your darkroom releases persistent heavy metal contamination regardless of how “green” your developer is.

2. Fixer efficiency (worthwhile) Extending fixer life through two-bath fixing or careful capacity management reduces the volume of silver-laden waste generated.

3. Developer choice (marginal) Lower-toxicity developers are preferable—ascorbic acid over hydroquinone, phenidone over metol—but the magnitude of benefit is small compared to items 1–3.

The discourse around sustainable darkroom practice has this hierarchy inverted. We debate caffenol versus Rodinal while ignoring fixer. Photographers feel virtuous about “natural” developers while—in jurisdictions with lax enforcement—pouring heavy metals down the drain. It's a kind of environmental theatre that lets people feel responsible without addressing the actual problem.

The Uncomfortable Conclusion

Here's the part that's hard to accept: there is no environmentally sustainable silver-gelatin photography without addressing the silver.

You cannot choose your way out of this problem. There's no “green fixer” alternative. The silver is intrinsic to the process—it's what you're photographing with, and some of it necessarily ends up in your fixer.

The only options are:

1. Recover the silver before discharge (eliminating ~95% of the heavy metal burden)
2. Dispose of fixer as hazardous waste (transferring the problem to licensed facilities)
3. Stop doing silver-gelatin photography (eliminating the problem at source)

Option 3 is obviously not what most analogue photographers want to hear. But it's worth stating plainly: non-silver alternative processes—cyanotype, Vandyke brown, gum bichromate, platinum/palladium—eliminate the silver problem entirely. They have their own environmental considerations (iron compounds, dichromates, precious metals), but they don't involve dissolving a heavy metal and needing to decide what to do with it.

If you're committed to silver-gelatin photography—and I understand the aesthetic and cultural reasons for that commitment—then silver recovery isn't optional. It's the price of responsible practice.

The next post in this series covers practical silver recovery methods for the home darkroom, along with water efficiency techniques and other interventions that actually matter. The good news: the most effective environmental action is also the cheapest. Steel wool costs pennies.

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A Note on Regulation and Enforcement

I've focused on environmental harm rather than legal compliance, because the two don't always align—and because regulatory frameworks vary enormously.

In some places (including where I'm based in Finland), spent fixer is unambiguously classified as hazardous waste, and municipal collection points exist to handle it. In others, home darkroom operators face little practical enforcement—wastewater authorities don't monitor individual households, and the volumes are small compared to commercial processors. Someone could pour spent fixer down the drain their entire photographic life and probably never face consequences.

But legality and ethics are different questions. The silver still reaches the environment. The aquatic toxicity remains what it is. The fact that no one is watching doesn't change the chemistry.

Some jurisdictions have strict formal requirements—Massachusetts requires photo processor certification; California classifies all silver-bearing waste as hazardous—that may seem disproportionate for home darkroom scales. Compliance can be onerous where infrastructure doesn't exist. But the underlying concern is legitimate.

My view: do what's right, not what's minimally required. If you can recover silver yourself, do it. If you can access hazardous waste collection, use it. The watershed doesn't care about jurisdiction.

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