Toxic heavy metal
A toxic heavy metal is any relatively dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts.[4][5] The term has particular application to cadmium, mercury and lead,[6] all of which appear in the World Health Organization's list of 10 chemicals of major public concern. Other examples include manganese, chromium, cobalt, nickel, copper, zinc, silver, antimony and thallium.[7]
Heavy metals are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health.
Contamination sources
Heavy metals are found naturally in the earth, and become concentrated as a result of human activities, or, in some cases geochemical processes, such as accumulation in peat soils that are then released when drained for agriculture.
Lead is the most prevalent heavy metal contaminant.
3CH
2)
4Pb, it was used extensively in gasoline during the 1930s–1970s.[17] Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels.[18] Although the use of leaded gasoline was largely phased out in North America by 1996, soils next to roads built before this time retain high lead concentrations. Lead (from lead(II) azide or lead styphnate used in firearms) gradually accumulates at firearms training grounds, contaminating the local environment and exposing range employees to a risk of lead poisoning.[19]
Entry routes
Heavy metals enter plant, animal and human tissues via air inhalation, diet, and manual handling. Motor vehicle emissions are a major source of airborne contaminants including arsenic, cadmium, cobalt, nickel, lead, antimony, vanadium, zinc, platinum, palladium and rhodium.[20] Water sources (groundwater, lakes, streams and rivers) can be polluted by heavy metals leaching from industrial and consumer waste; acid rain can exacerbate this process by releasing heavy metals trapped in soils.[21] Transport through soil can be facilitated by the presence of preferential flow paths (macropores) and dissolved organic compounds.[22] Plants are exposed to heavy metals through the uptake of water; animals eat these plants; ingestion of plant- and animal-based foods are the largest sources of heavy metals in humans.[23] Absorption through skin contact, for example from contact with soil, or metal containing toys and jewelry,[24] is another potential source of heavy metal contamination.[25] Toxic heavy metals can bioaccumulate in organisms as they are hard to metabolize.[26]
Detrimental effects
Heavy metals "can bind to vital cellular components, such as
Element | Acute exposure usually a day or less |
Chronic exposure often months or years |
Cadmium | Pneumonitis (lung inflammation) | Lung cancer Osteomalacia (softening of bones) Proteinuria (excess protein in urine; possible kidney damage) |
Mercury | Diarrhea Fever Vomiting |
|
Lead | Encephalopathy (brain dysfunction) Nausea Vomiting |
Anemia Encephalopathy Foot drop/wrist drop (palsy) Nephropathy (kidney disease) |
Chromium | Acute renal failure |
Pulmonary fibrosis (lung scarring) Lung cancer |
Arsenic | Nausea Vomiting Diarrhea Encephalopathy Multi-organ effects neuropathy |
Diabetes Hypopigmentation/Hyperkeratosis Cancer |
History
The toxic effects of arsenic, mercury and lead were known to the ancients but methodical studies of the overall toxicity of heavy metals appear to date from only 1868. In that year, Wanklyn and Chapman speculated on the adverse effects of the heavy metals "arsenic, lead, copper, zinc, iron and manganese" in drinking water. They noted an "absence of investigation" and were reduced to "the necessity of pleading for the collection of data".[30] In 1884, Blake described an apparent connection between toxicity and the atomic weight of an element.[31] The following sections provide historical thumbnails for the "classical" toxic heavy metals (arsenic, mercury and lead) and some more recent examples (chromium and cadmium).
Arsenic
Mercury
The first emperor of unified China,
Lead
The adverse effects of
Chromium
Cadmium
Remediation
In humans, heavy metal poisoning is generally treated by the administration of chelating agents.[60]
These are chemical compounds, such as CaNa
2EDTA (calcium disodium ethylenediaminetetraacetate) that convert heavy metals to chemically inert forms that can be excreted without further interaction with the body. Chelates are not without side effects and can also remove beneficial metals from the body. Vitamin and mineral supplements are sometimes co-administered for this reason.[61]
Soils contaminated by heavy metals can be remediated by one or more of the following technologies: isolation; immobilization; toxicity reduction; physical separation; or extraction. Isolation involves the use of caps, membranes or below-ground barriers in an attempt to quarantine the contaminated soil. Immobilization aims to alter the properties of the soil so as to hinder the mobility of the heavy contaminants. Toxicity reduction attempts to oxidise or reduce the toxic heavy metal ions, via chemical or biological means into less toxic or mobile forms. Physical separation involves the removal of the contaminated soil and the separation of the metal contaminants by mechanical means. Extraction is an on or off-site process that uses chemicals, high-temperature volatization, or electrolysis to extract contaminants from soils. The process or processes used will vary according to contaminant and the characteristics of the site.[62]
Benefits
Some elements otherwise regarded as toxic heavy metals are
See also
- Bento Rodrigues dam disaster
- Heavy metal detoxification
- Kingston Fossil Plant coal fly ash slurry spill
- Light metal
- Metal toxicity
Explanatory notes
Citations
- ^ Dewan 2008
- ^ Dewan 2009
- ^ Poovey 2001
- S2CID 201095843.
- ^ Srivastava & Goyal 2010, p. 2
- ^ Brathwaite & Rabone 1985, p. 363
- ^ "10 chemicals of public health concern". www.who.int. Retrieved 2021-10-09.
- ^ Wright 2002, p. 288
- PMID 14674528.
- ^ "Fear In The Fields -- How Hazardous Wastes Become Fertilizer -- Spreading Heavy Metals On Farmland Is Perfectly Legal, But Little Research Has Been Done To Find Out Whether It's Safe".
- ^ https://hazwastehelp.org/ArtHazards/glassworking.aspx Art Hazards
- ^ Harvey, Handley & Taylor 2015
- ^ Howell et al. 2012; Cole et al. 2011, pp. 2589‒2590
- ^ Finch, Hillyer & Leopold 2015, pp. 849–850
- ^ Aggrawal 2014, p. 680
- ^ Di Maio 2001, p. 527
- ^ Lovei 1998, p. 15
- ^ Perry & Vanderklein 1996, p. 336
- ^ Houlton 2014, p. 50
- ^ Balasubramanian, He & Wang 2009, p. 476
- ^ Worsztynowicz & Mill 1995, p. 361
- .
- ^ Radojevic & Bashkin 1999, p. 406
- PMID 24345102.
- ^ Qu et al. 2014, p. 144
- ^ Pezzarossa, Gorini & Petruzelli 2011, p. 94
- ^ Lanids, Sofield & Yu 2000, p. 269
- ^ Neilen & Marvin 2008, p. 10
- ^ Afal & Wiener 2014
- ^ Wanklyn & Chapman 1868, pp. 73–8; Cameron 1871, p. 484
- ^ Blake 1884
- ^ Dueck 2000, pp. 1–3, 46, 53
- ^ Dyer 2009
- ^ Whorton 2011, p. 356
- ^ Notman 2014
- ^ Zhao, Zhu & Sui 2006
- ^ Waldron 1983
- ^ Emsely 2011, p. 326
- ^ Davidson, Myers & Weiss 2004, p. 1025
- ^ New Scientist August 2014, p. 4
- ^ Pearce 2007; Needleman 2004
- ^ Rogers 2000, p. 41
- ^ Gilbert & Weiss 2006
- ^ Prioreschi 1998, p. 279
- ^ Hillman et al. 2015, pp. 3353–3354
- ^ Hillman et al. 2015, p. 3349
- ^ World Health Organization 2013
- ^ Torrice 2016
- ^ Harvey, Handley & Taylor 2015
- ^ Barceloux & Barceloux 1999
- ^ Newman 1890
- ^ Haines & Nieboer 1988, p. 504
- ^ National Research Council 1974, p. 68
- ^ Tovey 2011; Jones 2011; O'Brien & Aston
- ^ Vallero & Letcher 2013, p. 240
- ^ Vallero & Letcher 2013, pp. 239–241
- ^ Pritchard 2010
- ^ Mulvihill & Pritchard 2010
- ^ Cs uros 1997, p. 124
- ^ Blann & Ahmed 2014, p. 465
- ^ American Cancer Society 2008; National Capital Poison Center 2010
- ^ Evanko & Dzombak 1997, pp. 1, 14–40
- ^ Bánfalvi 2011, p. 12
- ^ Chowdhury 1987
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