Lady Astor: ‘Sir, if you were my husband , I would put arsenic in your tea!’

Churchill: ‘If I were your husband , I would drink it!’

This apocryphal joke is a reminder that arsenic is a potentially fatal poison. The phrase ‘mad as a hatter’ stems from the historical use of mercury by hatmakers, which could have neurotoxic consequences. Ironically, both these metals were also used therapeutically in the past to treat various diseases including syphilis. Arsenic and mercury, along with lead and cadmium, are often referred to as ‘heavy metals’, although it has been suggested that this term is misleading and should be replaced.1 These four toxic metal pollutants, which have no essential biological function, are established threats to human health,2 especially in low-income and middle-income countries (LMICs) where exposure levels are high.

Occupational exposure aside, general population sources of exposure to these toxic metals broadly include the air, soil, food and water. Rapid industrialisation and agricultural intensification in LMICs such as China have led to high toxic metal contamination of the soil, with implications for the human food chain.3 Importantly, these metals are non-degradable and thus environmentally persistent; a recent study showed, using lead isotope ratios, that air particles in London contained lead derived from petrol, even though lead in petrol had been phased out by 1999 in the UK.4

Epidemiological studies of toxic metal exposure and health have usually measured metal concentrations in blood or urine, or in groundwater wells in the case of arsenic, as proxies for chronic exposure. For lead, cadmium and arsenic exposure, there is considerable epidemiological evidence, backed up by mechanistic data, implicating these metals as cardiovascular risk factors.5 Cohort studies in US adults reported that higher concentrations of blood lead and urinary arsenic, even at low …