Editing Photographic processing (section)

== Environmental and safety issues ==
{{More citations needed section|date=August 2020}}
Many photographic solutions have high [[chemical oxygen demand|chemical]] and [[biochemical oxygen demand|biological]] oxygen demand (COD and BOD). These chemical wastes are often treated with [[ozone]], [[peroxide]] or [[aeration]] to reduce the COD in commercial laboratories.

Exhausted fixer and to some extent rinse water contain silver [[thiosulfate]] complex ions. They are far less toxic than free silver ion, and they become [[silver sulfide]] sludge in the sewer pipes or treatment plant. However, the maximum silver concentration in discharge is very often tightly regulated. Silver is also a somewhat precious resource. Therefore, in most large scale processing establishments, exhausted fixer is collected for silver recovery and disposal.

Many photographic chemicals use non-biodegradable compounds, such as [[EDTA]], [[DTPA]], [[Nitrilotriacetic acid|NTA]] and [[borate]]. EDTA, DTPA, and NTA are very often used as [[chelation|chelating agent]]s in all processing solutions, particularly in developers and washing aid solutions. EDTA and other [[polyamine]] polycarboxylic acids are used as iron ligands in colour bleach solutions. These are relatively nontoxic, and in particular EDTA is approved as a food additive. However, due to poor [[biodegradability]], these chelating agents are found in alarmingly high concentrations in some water sources from which municipal tap water is taken.<ref>{{cite journal|last=Fuerhacker|first=M. |author2=Lorbeer, G. |author3=Haberl, R.|title=Emission factors and sources of ethylene-diaminetetraacetic acid in waste water––a case study|journal=Chemosphere|date=30 June 2003|volume=52|issue=1|pages=253–257|doi=10.1016/S0045-6535(03)00037-7|pmid=12729709|bibcode=2003Chmsp..52..253F }}</ref><ref>{{cite book|last=Blair-Tyler|first=Martha|title=Look Before You Build|year=1995|publisher=United States Government Printing Office|location=Washington|url=https://books.google.com/books?id=z0fwAAAAMAAJ&q=EDTA++concentrations+water+sources+municipal&pg=RA1-PA131}}</ref>  Water containing these chelating agents can leach metal from water treatment equipment as well as pipes. This is becoming an issue in Europe and some parts of the world.{{Citation needed|date=November 2008}}

Another non-biodegradable compound in common use is [[surfactant]]. A common wetting agent for even drying of processed film uses Union Carbide/Dow Triton X-100 or octylphenol ethoxylate. This surfactant is also found to have estrogenic effect and possibly other harms to organisms including mammals.{{Citation needed|date=November 2008}}

Development of more biodegradable alternatives to the EDTA and other bleaching agent constituents were sought by major manufacturers, until the industry became less profitable when the digital era began.

In most amateur darkrooms, a popular bleach is [[potassium ferricyanide]]. This compound decomposes in the waste water stream to liberate [[cyanide]] gas.{{Citation needed|date=November 2008}} Other popular bleach solutions use [[potassium dichromate]] (a [[hexavalent chromium]]) or [[permanganate]]. Both ferricyanide and dichromate are tightly regulated for sewer disposal from commercial premises in some areas.

[[Borate]]s, such as [[borax]] (sodium tetraborate), [[boric acid]] and sodium metaborate, are toxic to plants, even at a concentration of 100 ppm. Many film developers and fixers contain 1 to 20 g/L of these compounds at working strength. Most non-hardening fixers from major manufacturers are now borate-free, but many film developers still use borate as the buffering agent. Also, some, but not all, alkaline fixer formulae and products contain a large amount of borate. New products should phase out borates, because for most photographic purposes, except in acid hardening fixers, borates can be substituted with a suitable biodegradable compound.

Developing agents are commonly [[hydroxylation|hydroxylated]] [[benzene]] compounds or aminated benzene compounds, and they are harmful to humans and experimental animals. Some are [[mutagen]]s. They also have a large chemical oxygen demand (COD). [[Ascorbic acid]] and its isomers, and other similar sugar derived reductone reducing agents are a viable substitute for many developing agents. Developers using these compounds were actively patented in the US, Europe and Japan, until the 1990s but the number of such patents is very low since the late-1990s, when the digital era began.

Development chemicals may be recycled by up to 70% using an absorber resin, only requiring periodic chemical analysis on pH, density and bromide levels. Other developers need ion-exchange columns and chemical analysis, allowing for up to 80% of the developer to be reused. Some bleaches are claimed to be fully bio-degradable while others can be regenerated by adding bleach concentrate to overflow (waste). Used fixers can have 60 to 90% of their silver content removed through electrolysis, in a closed loop where the fixer is continually recycled (regenerated). Stabilizers may or may not contain [[formaldehyde]].<ref>{{Cite web |title=Technical Bulletin C41 |url=https://www.fujifilm.eu/fileadmin/countries/europe/United_Kingdom/Photofinishing_data_files/Technical_bulletins/TB_C41_E13_09-10.pdf |archive-url=https://web.archive.org/web/20200814103307/https://www.fujifilm.eu/fileadmin/countries/europe/United_Kingdom/Photofinishing_data_files/Technical_bulletins/TB_C41_E13_09-10.pdf |archive-date=14 August 2020 |website=Fujifilm}}</ref>