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Discuss about the Occupation Health and Safety.
Silver is one of the rare metals found in earth. It is found in the form of soft silver naturally. Silver and silver compounds are found at various working sites present in the soil, air or water that are hazardous to human health.
Silver dust particles and soluble compounds of silver lead to a condition called Argyria. It is caused by exposure to silver and silver containing materials. It results in staining of the skin and mucosal membrane. It occurs due to deposition of silver on the dermal layer as a result of exposure to industrial chemicals or medicines containing salts of silver and other silver compounds. The workers who are vulnerable to the hazardous substance are involved in various industrial activities like mining and refining of silver, manufacturing of silver utensils, metal alloy, phorographic processings and so on. The exposure to silver affect the respiratory tract and cause serious ailments like mild or chronic bronchitis in workers exposed to manifacturing of silver nitrate (1).
The toxicity profile of silver includes genotoxicity, reproductive toxicity, developmental toxicity, immunotoxicity and neurotoxicity.
The various sources of exposure, especially exposure to silver in occupational spaces, occupational exposure limits that are applicable as per the Occupational Health and Safety Administration (OSHA), regulations, monitoring strategies, sample analysis and toxicolological profile of silver, its biotransformation, absorption, distribution, metabolism, storage and trarget sites are outlined.
Sources of silver exposure includes inhalation of silver containing substances at workplace, silver compounds present in sources of water for drinking purpose, handling silver materials at workplace and silver dust particles that can cause eye irritation in workers (2).
Other sources are using silver in medications; activities that involve silver exposure are jewelry making and soldering. The occupational sources of silver exposure consist of mining and ore purification activities involving liberation of silver particles, manufacturing of silver nitrate used in photography, plating, mirrors, inks, and dyes, germicides, antiseptics, reagents of analytical standards, glass manufacturing, silver plating and laboratory reagents (3).
Sources also include liberation of the materials containing silver while manufacturing and casting alloys, silver metal fabrication.
During the photo chemicals, paints, pigments and silver powder manufacturing, some silver particles liberating from the site are also regarded as the sources of silver exposure.
The occupational sources of silver exposure also include elemental silver exposure, exposure to silver nitrate and silver oxides. The radiographic materials and photographic articles involve certain solution in their processing that contains silver. The dental amalgams, creams like Sulfadiazine cream and solutions for relieving burns also contain silver compounds.
Occupational Exposure Limits (OELS) are referred as limitation values required for prevention of the occupational health hazards or other factors related to the workplace risk that affect adversely the health of the workers involved in chemicals related works and have high level of exposure to them (4).
The short-term exposure limits are generally set for 15 minutes. They are set for short duration of exposure to harmful chemicals and fumes.
According to Occupational Health and Safety Administration (OSHA), the silver and silver containing compounds have regulatory limit of 0.01mg/m3 and 0.01 ppm (5).
The recommended limit of silver and silver containing substances is prescribed according to NIOSH REL (National Institute for Occupational Safety and Health recommended exposure limit). Metals, dusts and fumes have a recommended limit of 0.1mg/m3. The recommendation for the exposure limit in case of soluble silver compounds is 0.01mg/m3. According to CAL/OSHA PEL, the permissible exposure limit is 0.01 mg/m3 for potential occupational carcinogens (6).
Legislation: According to Emergency and Community Right-to-know Act, section 313, silver is considered and enlisted as a toxic chemical.
Regulations for air: According to OSHA CFR 1910. 1000, it is stated that the maximum limit of silver is 0.01mg/m3.
Regulations for water: Drinking water: EPA 40 CFR 141 states the maximum limit is 0.05 mg/L (7).
As per Australia PEL, CAS No. 7440-22-4, Silver and soluble silver compounds have Time Weighted Average (TWA) of 0.01 mg/m3 for 8 hours (8).
Singapore PEL, Work Safety and Health Act, section 65 states that there must be a medical practitioner designated for the workplace, personnel must be fit for the work and proper training must be provided to them. Medical examination of the workers is a must as stated by regulation 4 and 5 (9).
Monitoring strategies: The Health and Safety Executive (HSE) provide a basic guidance towards monitoring strategies of harmful toxics.
The monitoring strategies are required for assessment of the risk to ensure that they comply with the workplace exposure limits (WEL). It is also involves health monitoring and setting up of workplace standards (10).
The monitoring strategy involves:
Personal monitoring: It consists of measurement of exposure levels of the personnel and workers involved in the hazardous activity, detection and monitoring of the emission source source, determination of the concentration levels of the toxics present in air of the breathing area.
Fixed place monitoring: The sources at fixed places can also be monitored for silver or such chemical presence. Though fixed place sampling cannot help in determining risk in the entire workspace, but it can be helpful for assessing risk in individual’s health (11).
Moreover, a scheme on protection of personal health can be organized for regular monitoring, assessment, training of workers and evaluation.
Monitoring of personal protective equipment, its functionality, hygiene and maintenance must be conducted. Monitoring for contamination of personnel clothing, storage and cleaning techniques should also be made.
Monitoring is done for ensuring that sanitation is maintained well within the workplace. Activities like smoking and eating in the working space also need to be controlled.
Figure 1-Schematic approach towards strategic monitoring of hazardous substances
(Source: www.hse.gov.uk)
Sample analysis: The sample analysis for silver is done by the analytical method using biological and environmental samples.
The samples with silver materials present in traces (approximately about 10-6 to 10-9) can be detected by various analytical methods. The methods include atomic emission spectroscopy with high frequency torch, neutron activation analytical technique, flameless atomic absorption spectroscopy, flame atomic absorption spectroscopy and micro-cup atomic absorption spectroscopy. Among all other methods, the most commonly used method for detection of trace amount of silver in biological samples is atomic absorption spectroscopy. Flameless atomic absorption spectroscopy is also used as it has high detection ability of samples containing silver in gram or microgram.
The analytical methods like atomic absorption spectroscopy and plasma emission spectroscopy are extensively being used for detecting silver materials in environmental samples like air, water and soil. Flame atomic absorption spectroscopy is used for identification of silver substance in waste materials. Flameless atomic spectroscopy technique is used for detection of the silver containing substances in water samples. This is an extremely sensitive analytical method for analysis of environmental samples. Paper chromatography and thin layer chromatography are also used for determination of the traces of silver nitrate in surface and fresh water. Atomic absorption spectroscopy is also used for analysis of contaminants present in soil samples (12).
Toxicology associated with silver are:
Gentotoxicity: Though silver does not undergo mutation, however, it can result in breakdown of DNA strands that has an impact on constancy of the replication procedure of the genetic material.
Reproductive toxicity: Silver deposition does not affect the reproductive system in either of the sexes, but injection through subcutaneous route of administration may result in deterioration of the tissues and morphology of the testicles.
Developmental toxicity: The increased levels of silver materials in fetal tissues may result in malformation and abnormalities in the fetus.
Immunotoxicity: Exposure to silver materials to the dermal surface may cause some reaction and hypersensitivity in individuals.
Neurotoxicity: The exposure to silver orally can cause changes in neuroanatomical profile resulting in deterioration of health (13)
Biotransformation refers to any modification or alteration made chemically by some organisms on a chemical substance. Biotransformation consists of two phases of reactions.
Phase I- It involves oxidation, reduction and hydrolysis (14).
Phase II- It involves conjugation reactions
The condition, Argyria is a rare dermal disease mainly caused by exposure to silver and silver containing compounds. It is considered a consequence of a complex biotransformation mechanism. It is mainly caused by oral ingestion of silver substances. The mechanism in which the biotransformation takes place is a complex process. The silver ingested through oral route undergoes oxidation to form salt as the resultant. This resultant salt form undergoes absorption in the gastrointestinal tract and is distributed through systemic circulation into the dermal membrane. The dermal layer is composed of cells and in these cells it may undergo further biotransformation reactions. These reactions may also involve photo reduction of the silver complex forms. The complex forms if undergoes further complexation reactions with metals like Selenium, may result in permanent accumulation of silver in the tissues involved in it and hence the silver gets deposited on the skin (15).
Absorption: The absorption of silver and silver containing substances occurs through inhalation, oral as well as dermal route.
The inhalation and dermal route are the two main routes through which the exposure of the contaminants takes place. In case of long-term exposure to the silver substances, the route through which exposure occurs is the dermal route. Exposure to silver occurs through ingestion of the substance which results in its absorption. The rate and extent to which the absorption of the contaminant takes place depends on the transit time which is the time taken by the substance to travel along the gastrointestinal tract. The absorption can also occur through the skin. The exposure to complexes of silver may lead to Argyria. The absorption also takes place through damaged and burnt skin. The medicines containing 0.5% silver nitrate may also serve as a source of absorption of silver on the dermis (16).
Distribution: The silver compounds ingested through oral route or inhaled undergo distribution. The elemental silver also gets distributed that are inhaled or ingested orally. The extent of distribution in the organs varies. The extent to which the metallic silver is distributed in bladder and bile is around 0.03%, its 0.028% in the intestinal region, 0.09% in heart, stomach 0.12% and muscle 0.007% (17). The distribution of silver takes place following the dermal route. The silver exposure through topical application of medications like burn creams may result in distribution of the silver substance into spleen, heart, kidney and bones.
Accumulation/ Metabolism: Precipitation of silver salts like silver chloride, silver phosphate may result in silver deposition into the tissues. These salt forms are transformed into soluble silver as the resulting substance. The soluble forms include sulfides and aluminates. They form complexes by binding with amino acids, carboxylic groups found in genetic materials (RNA and DNA) and proteins. In addition to it they also may undergo reduction by reacting with ascorbic acids and catecholamine to form metallic silver. The resultant silver metal undergoes oxidation. The tissues carry it out. They are accumulated as silver sulfide, which is a black colored product. The formation of this resulting substance imparts black coloration to the skin and the individuals are detected with Argyria (18).
Excretion: The radioactive silver substance undergoes rapid clearance from the lungs preliminarily by ciliary actions resulting in removal in the form of feces. The removal of silver from liver occurs by billiary excretion.
Storage and target organs: The primary storage and target organ is skin. Primarily the silver exposure at occupational site mainly affects the skin. It also gets into the body by inhalation and ingestion. The exposure to a photochemical material site or under such influences result in silver deposition in the dermis. This results in blue-black coloration of the skin. The silver exposure through inhalation results in accumulation of the substance in lungs. They also get accumulated in the liver, spleen, heart, intestine through various routes of exposure of the contaminant substance (17).
Conclusion
Silver is metal rarely found on earth. It is used for making silver ornaments, photographic plates, as medicines and such other purposes. These activities are related to various hazards to the workers involved in handling of silver materials. Silver deposition in the skin leads to a rare condition called Argyria characterized by discoloration of the dermis. There are various sources of silver exposure at workplace. Occupational sources of silver also include silver plating, dyes, ink, pigments, mining, refining and other activities.
Occupational Safety and Health Administration set the occupational and prescribed exposure limit. This also serves as regulatory guideline. The monitoring approaches to toxic chemicals involve assessment of the toxic substance at the worker’s breathing zone as well as the source area of the contaminant. Environmental and biological samples are analyzed by a series of analytical technique involving various spectroscopy and chromatographic principles. Argyria is a result of biotransformation involving complex processes. Silver is an indispensable part as it has a widespread area of implementation.
Therefore, adopting proper monitoring, managing and control measures is necessary to reduce the exposure levels and safeguard the lives of the people engaged at occupational sites that deal with silver in numerous ways.
References:
1.Bakand S, Hayes A. Toxicological considerations, toxicity assessment, and risk management of inhaled nanoparticles. International Journal of Molecular Sciences. 2016 Jun 14;17(6).
2.Berlin A, Yodaiken RE, Hanman WA, editors. Assessment of toxic agents at the workplace: roles of ambient and biological monitoring. Springer Science & Business Media; 2012 Dec 6.
3.Bretherick L. Bretherick's handbook of reactive chemical hazards. Elsevier; 2013 Oct 22.
4.Beer C, Foldbjerg R, Hayashi Y, Sutherland DS, Autrup H. Toxicity of silver nanoparticles—nanoparticle or silver ion?. Toxicology letters. 2012 Feb 5;208(3).
5.Harbison RD, Bourgeois MM, Johnson GT. Hamilton and Hardy's industrial toxicology. John Wiley & Sons; 2015 Feb 9.
6.Bergeson LL, Cole MF. Regulatory Implications of Nanotechnology. Biointeractions of Nanomaterials. 2014 Jul 29.
7.Dave V, Khirwadkar P, Dashora K. A review on biotransformation. Indian Journal of Research in Pharmacy and Biotechnology. 2014 Mar 1;2(2).
8.Molina-Hernandez AI, Diaz-Gonzalez JM, Saeb-Lima M, Dominguez-Cherit J. Argyria after silver nitrate intake: Case report and brief review of literature. Indian journal of dermatology. 2015 Sep;60(5):520.
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10.Munger MA, Radwanski P, Hadlock GC, Stoddard G, Shaaban A, Falconer J, Grainger DW, Deering-Rice CE. In vivo human time-exposure study of orally dosed commercial silver nanoparticles. Nanomedicine: Nanotechnology, Biology and Medicine. 2014 Jan 31;10(1).
11.Lee JH, Ahn K, Kim SM, Jeon KS, Lee JS, Yu IJ. Continuous 3-day exposure assessment of workplace manufacturing silver nanoparticles. Journal of Nanoparticle Research. 2012 Sep 1;14(9).
12.www.atsdr.cdc.gov. 2016 [cited 27 September 2016] Available from: https://www.atsdr.cdc.gov/toxprofiles/tp146.pdf
13.Peters TM. Managing Risks in Occupational Environments. Nanotechnology: Health and Environmental Risks. 2012 Nov 12.
14.www.ilo.org. 2016 [cited 27 September 2016] Available from: http://www.ilo.org/dyn
15.Sarazin P, Burstyn I, Kincl L, Lavoué J. Trends in OSHA Compliance Monitoring Data 1979–2011: Statistical Modeling of Ancillary Information across 77 Chemicals. Annals of Occupational Hygiene. 2016 Jan 4.
16.www.dhss.delaware.gov. 2016 [cited 27 September 2016] Available from: http://dhss.delaware.gov/dhss/dph/files/silverfaq.pdf
17.www.safeworkaustralia.gov.au. 2016 [cited 27 September 2016] Available from: http://www.safeworkaustralia.gov.au
18.www.osha.gov. 2016 [cited 27 September 2016] Available from: https://www.osha.gov/dsg/annotated-pels/tablez-1.html
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