The dangers of lead are not exactly up for debate: Lead exposure early in life has consistently been linked to a number of developmental effects in kids, from lower IQ to more school suspensions. But early lead exposure can also bring on behavioral and emotional problems, including the ones that aren’t so obvious to the observer — like depression and anxiety — according to a new study.

Researchers from the University of Pennsylvania followed 1300 Chinese children from the time they were toddlers until they were six years old. In China, lead exposure comes mostly from air pollution, rather than from paint and plumbing as it does in the United States.

When the children were between three and five years old, the team measured the level of lead in their blood. At age six, the children’s teachers and parents filled out questionnaires about their behavioral and emotional health.

Children with higher blood levels of lead showed more ‘internalizing’ issues, like anxiety and depression.

The average lead level in the Chinese children was 6.4 micrograms per deciliter, which is slightly higher than the 5 micrograms per deciliter level that’s considered normal. Most previous studies looked at the effects of having levels over 10 micrograms per deciliter.

Kids' emotional and behavioral problems rose as levels of lead in the blood increased. In particular, children with higher blood levels of lead showed more “internalizing” issues, like anxiety and depression. Previous studies had mainly looked at links between lead and “externalizing” problems like bullying and other forms of aggression, so the new study is important because it shows another potential risk from early lead exposure.

There are, however, two important caveats. First, only the parents’ and teachers’ assessments were included — not those of healthcare professionals — so it's not clear that the children would have been diagnosed with behavioral or emotional problems. And, second, the study was relatively short-term, so we can't be sure without longer-term studies whether and for how long the effects persist.

But the study does provide even more evidence that there is simply no safe level of lead exposure — a reality that previous research has confirmed. Children’s brains are especially susceptible to environmental effects since they are still developing, and high levels of toxins can alter the course of development.

If you’re pregnant or have children and believe your home may have lead paint or other materials, have it checked out. When it comes to the brain development of your children, it’s always better to err on the side of caution. No one knows how little lead exposure is too much.

The study is published in JAMA Pediatrics.