Waste X-ray films secondary resource
Used silver-bearing radiographic films obtained from medical facilities, comprising a gelatin-silver emulsion on a polymer base. The curated feeds are discarded X-ray films, not unused film stock, photographic processing liquids, elemental silver or all photographic wastes. Laboratory studies distinguish microbial-enzyme stripping of the emulsion from subsequent thermal production of silver metal. No constituent criticality designation or industrial deployment is inherited.
Microbial & Biochemical Mechanisms (2)
Gelatin-silver layer stripping by fungal cell-free culture supernatant
separation
Microbial
Associated Organisms:
Conidiobolus coronatus (NCBITaxon:34488)
Crude cell-free supernatant from the source-designated Conidiobolus coronatus ATCC PTA-4132 culture removed the gelatin layer and released silver-bearing material. Dose dependence, a low zero-enzyme response and protein/hydroxyproline release support proteolytic stripping; microbial silver reduction, metal solubilization or a purified enzyme mechanism was not demonstrated. Living fungus was used to produce the preparation, not applied directly to the films.
Experimental Context & Analytical Limits:
Shankar2010 obtained used films from a local medical centre, washed them with water and ethanol, dried them at 40 degrees C for 30 min and cut 2 by 2 cm pieces. Enzyme preparation used 72 h growth in MGYP broth with 2% w/v soybean meal, then centrifugation at 8000 g for 20 min at 4 degrees C. The paper refers culture-production details to prior work; no independent strain authentication was performed here. Stripping assays generally used 1 g film in 10 mL crude preparation at pH 10 and 40 degrees C with shaking. The separate silver assay used 5 g in 50 mL, 1.35 U/mL protease and 200 rpm, followed by acid digestion of the slurry and atomic absorption analysis. Activity units are source assay units, not an enzyme mass or units directly comparable across studies. Independent replicate counts and variability are not reported.
Shankar2010 obtained used films from a local medical centre, washed them with water and ethanol, dried them at 40 degrees C for 30 min and cut 2 by 2 cm pieces. Enzyme preparation used 72 h growth in MGYP broth with 2% w/v soybean meal, then centrifugation at 8000 g for 20 min at 4 degrees C. The paper refers culture-production details to prior work; no independent strain authentication was performed here. Stripping assays generally used 1 g film in 10 mL crude preparation at pH 10 and 40 degrees C with shaking. The separate silver assay used 5 g in 50 mL, 1.35 U/mL protease and 200 rpm, followed by acid digestion of the slurry and atomic absorption analysis. Activity units are source assay units, not an enzyme mass or units directly comparable across studies. Independent replicate counts and variability are not reported.
Curated Evidence Points:
Support
Source:
shankar2010
Methods pp.61-63 and Figures 1-3 support the conditions and temperature, pH and dose responses; Figure 3 includes a 0 U/mL comparator that remains near baseline. The pH/temperature series reports complete layer removal at 40 degrees C and pH 10 in 6 min with 1.35 U/mL. This is an operational stripping endpoint; percentage hydrolysis is normalized to maximum turbidity, not a measured percentage of silver recovered.
Partial
Source:
shankar2010
The time-course Methods p.62 specifies 0.9 U/mL whereas Figure 4a labels 1.35 and 2.7 U/mL; the disputed dose-specific series is not combined with the other arms. Figure 3 was sampled every 5 min, so its text's proposed 6-min completion was explicitly not measured in that arm. Table 1 separately reports four successive film batches at 0.90 U/mL taking 6, 10, 14 and 20 min, including the first use; lower-dose preparations lose stripping capacity sooner. This does not establish four additional reuses or constant performance.
Partial
Source:
shankar2010
Silver analysis p.68 reports 3.87% w/w of solid sludge and 0.2% w/w relative to starting film mass. These denominators differ from recovery of initial silver inventory, which was not independently established for the tested feed. The introduction's 1.5-2% silver range is background, not its feed assay. The statement that metal or AgCl was recovered has no corresponding isolation protocol or product characterization in this paper; the accepted result is silver-bearing hydrolysate and stripped film. No whole-process mass balance, comparative energy assessment or deployment follows.
Bacterial enzyme stripping followed by separate abiotic silver smelting
recovery
Microbial
Associated Organisms:
Bacillus spizizenii ATCC 6633 = JCM 2499 (NCBITaxon:703612)
Culture-derived cell-free enzyme extract stripped the gelatin-silver layer, after which drying and borax-assisted smelting produced a silver product. Microbial involvement concerns enzyme production and stripping; the high-temperature metal isolation was abiotic. The source calls the culture Bacillus subtilis ATCC 6633; current ATCC and NCBI records map that designation to Bacillus spizizenii, without reauthenticating the historical Ege University stock.
Experimental Context & Analytical Limits:
Nakiboglu2001 used films from Ege University's medical-faculty hospital radiology department. The culture was grown in modified Horikoshi medium supplemented with 1% gelatin, at 30 degrees C and 200 rpm for 24 h; a further transfer is described without an independently specified final culture volume. Centrifugation at 10000 rpm for 10 min at 4 degrees C provided the cell-free extract. Film pieces were washed with water/ethanol, dried at 40 degrees C for 30 min and cut to 4 by 4 cm. The reported recovery run treated 70 pieces successively in 100 mL stock extract at pH 8 and 50 degrees C with stirring, then dried the slurry and smelted it with borax at 1100 degrees C. The preparation's measured casein-assay activity was 22.35 U/mL. No enzyme-free film comparator or initial silver-inventory assay is reported, and the downstream furnace hold time and borax loading are not specified.
Nakiboglu2001 used films from Ege University's medical-faculty hospital radiology department. The culture was grown in modified Horikoshi medium supplemented with 1% gelatin, at 30 degrees C and 200 rpm for 24 h; a further transfer is described without an independently specified final culture volume. Centrifugation at 10000 rpm for 10 min at 4 degrees C provided the cell-free extract. Film pieces were washed with water/ethanol, dried at 40 degrees C for 30 min and cut to 4 by 4 cm. The reported recovery run treated 70 pieces successively in 100 mL stock extract at pH 8 and 50 degrees C with stirring, then dried the slurry and smelted it with borax at 1100 degrees C. The preparation's measured casein-assay activity was 22.35 U/mL. No enzyme-free film comparator or initial silver-inventory assay is reported, and the downstream furnace hold time and borax loading are not specified.
Curated Evidence Points:
Support
Source:
nakiboglu2001
Experimental pp.350-351 and Results p.352 distinguish the upstream biological preparation from thermal recovery. The authors report 0.4013 g silver product and potentiometric purity 99.16 plus or minus 0.11%, specified as a 95% confidence level with N=5. This is product composition, not 99.16% recovery of the feed silver or five independent process replicates. Table 2 separately measures eleven trace impurities by ICP-MS; it is not a complete impurity mass balance or proof of semiconductor-grade silver.
Partial
Source:
nakiboglu2001
Figure 1 tests the pH response at 30 and 40 degrees C, while the recovery run uses 50 degrees C. Table 1 reports declining capacity at 60 degrees C, but its speed/capacity denominators cannot be reconciled directly with the stated 4-by-4-cm pieces and 100-mL run; those numerical capacities are not adopted. The 0.36 mg/cm2 value is calculated from the recovered product, not a separate starting-film silver assay. No total-inventory extraction yield, exclusive enzyme causality, industrial operation or environmental superiority is established; the authors themselves retain the high-temperature burning step as a disadvantage.
Context_only
Source:
atcc6633
The current collection entry identifies ATCC 6633 as Bacillus spizizenii strain NRS 231, deposited as Bacillus subtilis. This nomenclatural mapping supports the linked organism label; collection metadata and later genome sequencing are not evidence that the historical assay stock was independently authenticated.
Sources & References
-
shankar2010: Shankar, More and Laxman (2010). Recovery of Silver from Waste X-Ray Film by Alkaline Protease from Conidiobolus coronatus. Kathmandu University Journal of Science, Engineering and Technology 6(1):60-69; original published PDF, Methods pp.61-63, Figures 1-4, Table 1 and silver analysis p.68. Legacy DOI 10.3126/kuset.v6i1.3311; printed March 2010 issue rather than Crossref's anomalous 1970 date.
https://nepjol.info/index.php/KUSET/article/download/3311/2851 (accessed 2026-10-14) -
nakiboglu2001: Nakiboglu, Toscali and Yasa (2001). Silver Recovery from Waste Photographic Films by an Enzymatic Method. Turkish Journal of Chemistry 25:349-353; complete original institutional copy, Experimental pp.350-351, Figure 1, Tables 1-2 and product measurements p.352. Publisher lists no assigned DOI.
https://acikerisim.balikesir.edu.tr/bitstreams/2aa318e5-ec84-4407-b611-8ecd7586b136/download (accessed 2026-10-14) -
ncbi_coronatus: NCBI Taxonomy 34488: Conidiobolus coronatus, species; not identification of the assay stock
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=34488 (accessed 2026-10-14) -
ncbi_atcc6633: NCBI Taxonomy 703612: Bacillus spizizenii ATCC 6633 = JCM 2499; strain record
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=703612 (accessed 2026-10-14) -
atcc6633: ATCC 6633: Bacillus spizizenii, strain NRS 231; deposited as Bacillus subtilis, formerly Bacillus subtilis subsp. spizizenii. Current culture name does not independently authenticate the historical experimental stock.
https://www.atcc.org/products/6633 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T19:41:46Z |
Codex (GPT-6; Codex) | CREATE | Added the medical waste-film resource from two complete primary studies, distinguishing fungal enzyme stripping and bacterial enzyme stripping followed by abiotic smelting. Preserved source-dose discrepancies, uncertain controls and denominators, product-purity scope and current taxonomic mappings. Independent scientific review is separate. |
Record source: data/records/waste-x-ray-films.yaml