From awful convulsions and paralysis in wildlife, to heartbreaking miscarriages in humans, the physical dangers of lead exposure are well established.

As a neurotoxin, lead has also been implicated in mental and developmental problems, including lowering IQ. A new review suggests early-life lead exposure may be leading to increased risks of criminal behavior much later in life.

"Policy action to prevent lead exposure is of utmost importance," environmental health scientist Maria Jose Talayero and colleagues from the George Washington University write in their paper.

"Our research shows an excess risk for criminal behavior in adulthood exists when an individual is exposed to lead in utero or during childhood."

They found an overall link between lead exposure and the later development of aggressive or hostile traits, including criminal records. But, as the team only found 17 papers that met their criteria, focusing on people at an individual level, they could not establish the strength of this association.

Their findings, however, are in line with population-level studies, which have suggested reducing lead exposure contributed to a reduction in crime levels in the US during the 20th century.

Talayero and team note more research is needed to further explore what is happening on the individual level, but in light of lead's known biological impacts and population-level associations, the team is adamant that policymakers should be acting now.

"All of these results point to a significant association between lead exposure and hostile, antisocial, and aggressive behavior – traits that strongly correlate with later criminal behavior," they write in their paper.

Lead accumulates in our bodies over time, and there is no known safe level of exposure. Children are particularly vulnerable.

"Children do not absorb or metabolize lead in the same way as adults and are far more susceptible to the negative impacts of lead exposure due to a hyper-permeable blood-brain barrier and rapidly developing organ systems," Talayero and colleagues explain.

In the 20th century, the main source of lead exposure was leaded gasoline used to fuel cars. In the US alone, this meant around 170 million adults with increased risks of mental illness, cardiovascular problems, and neurodegenerative diseases just from exposure during their childhoods.

Despite efforts to reduce childhood lead exposure, a recent study found nearly half a million US children have detectable lead levels in their blood.

Ongoing sources of lead contamination include heavy industry and aging infrastructure, like the lead leaching pipes that caused the devastating lead poisoning of Flint's drinking water in Michigan in 2014.

Lead exposure can also arise from less expected sources, including children's toys from unregulated markets, old paint, aviation fuel, and lead-glazed food containers.

When investigating frighteningly high levels of the neurotoxin in rural Bangladeshi children, researchers were astonished to discover it was being used as an additive to the region's most popular spice, turmeric, to enhance the yellow color.

While it is often the most disadvantaged people who are exposed to the neurotoxin, this new review emphasizes that what we allow to occur to those who lack the means to protect themselves could impact our entire society.

"Preventing lead exposure is crucial to safeguard public health and promote a safer society for all," the team concludes.

This research was published in PLOS Global Public Health.