Exposure to environmental pollutants kills 1.7 million children under the age of five each year, according to two reports released on Monday by the World Health Organization (WHO). Worldwide, more than one in four deaths among children under the age of five are attributable to environmental hazards such as indoor and outdoor air pollution, contaminated water, and poor sanitation, the WHO reports.

The first report finds that some of the most common causes of death among young children — diarrhea, malaria, and pneumonia — can be prevented through providing access to safe water and clean cooking fuels, and other efforts to reduce environmental risks. The second report details the impact that exposure to polluted environments has had on child mortality.

“A polluted environment is a deadly one.”

“A polluted environment is a deadly one — particularly for young children," WHO Director-General Margaret Chan said in a statement. "Their developing organs and immune systems, and smaller bodies and airways, make them especially vulnerable to dirty air and water."

According to the second WHO report, 570,000 children under the age of five die every year from respiratory infections linked to indoor and outdoor air pollution, and second-hand smoke; 361,000 die every year from diarrhea, because of poor sanitation, hygiene, and limited access to safe drinking water; and 270,000 die during their first month from conditions that could have been prevented through improved sanitation, access to safe water, and reduced air pollution. Another 200,000 deaths from malaria could have been prevented through mosquito control and safer water management, the report finds.

The WHO reports detail the long-term effects that environmental pollution can have on childrens’ health, as well. Children exposed to air pollution and second-hand smoke have an elevated risk of developing pneumonia and chronic respiratory problems, such as asthma. Increasing volumes of electronic waste from disposed smartphones and other devices can expose children to toxins linked to reduced intelligence, lung damage, and cancer, the WHO says. The volume of so-called e-waste is expected to reach 50 million metric tonnes by 2018 — a 19 percent increase from 2014.

In 2013, the International Agency for Research on Cancer (IARC), the WHO’s cancer arm, classified outdoor air pollution as a carcinogen for humans, reporting links to lung and bladder cancer. In September 2016, the WHO said that more than 90 percent of the world’s population lives in areas where air pollution exceeds levels considered safe for humans.

Climate change has heightened risk factors, as well; rising temperatures and CO2 levels has led to increased pollen counts, which is linked with asthma prevalence among young children. Between 11 and 14 percent of children under the age of five currently suffer from asthma-related symptoms, and 44 percent of those cases are attributable to environmental factors, the WHO says.

To mitigate these risks, the WHO has called on governments to reduce indoor and outdoor air pollution, protect pregnant women from second-hand smoke, and provide safe water and sanitation.