heavy metals

Introduction

heavy metals are generally regarded as toxins, particularly as they tend to be poorly eliminated and thus tend to accumulate with chronic exposures resulting in cellular toxicities
there is no formal definition of a heavy metal but tends to be context-driven such as in toxicology, but they are generally metals with a density > 10 g/cm³ such as lead (11.3g/cm³) and mercury (13.5g/cm³) although arsenic is generally included as it is toxic despite it being a metalloid and only at 5.7 g/cm³ , hexavalent chromium is 7.2 g/cm³ and cadmium is 8.7g/cm³. Essential metals tend to be excluded even though “heavy” unless in toxic amounts eg. zinc (7.1g/cm³), iron (7.9g/cm³) and copper (9g/cm³)

Lead (Pb)
- classic cause of neurotoxicity, hematologic and renal injury, especially in children and in occupational exposure.
- see lead poisoning
- lead plumbing pipes were widely used in western cities from the late 1800s
- toxicity risks became known in the early 1900s
- partly as infants often bit and chewed on the painted cot sides, lead paint was gradually banned in western regions from 1960's and particularly by late 1970's although Australia only tightened rules to prohibit > 0.1% lead in paint in 1992
- in the late 1980's, many western countries banned lead in the use of lead pipes, solder (over 0.2% lead), and flux in public water systems and residential/non-residential plumbing but existing systems in older homes have still not be fully replaced
Mercury (Hg)
- elemental, inorganic, and organic forms; neurotoxic, nephrotoxic, with fetal CNS vulnerability.
- see mercury poisoning
Arsenic (As)
- technically a metalloid, but universally grouped with heavy metals in toxicology; systemic toxicant and carcinogen.
Cadmium (Cd)
- kidney and bone toxicity, carcinogenic; often from industrial sources and cigarette smoke.
Chromium (Cr)
- especially hexavalent chromium; respiratory, renal toxicity and carcinogenicity

Aluminum (Al)
- often grouped as a toxic metal in clinical and lab toxicology references.
Thallium (Tl)
- highly toxic, causes severe neurological and gastrointestinal symptoms.
Beryllium (Be)
- carcinogenic, causes chronic beryllium disease.
- see beryllium oxide inhalation
Nickel (Ni), Cobalt (Co)
- occupational and environmental exposures linked with neurotoxicity and/or carcinogenicity.
Antimony (Sb), Tin (Sn as organotin), Silver (Ag)
- recognized for specific toxic effects, particularly in environmental and occupational settings