A girl wading through mountains of trash; a boy up to his neck in toxic waters—these photos show just some of the children exposed to potentially fatal environmental conditions.

At least one in four deaths of children under five, almost 1.7 million children, can be attributed to pollution, according to a newly released report from the World Health Organization (WHO).

A lack of access to potable drinking water leaves children vulnerable to preventable diseases such as diarrhea, malaria, and pneumonia. About 570,000 children also suffer from exposure to air pollutants and indoor pollution, from such causes as cigarette smoke and cooking fires, leading to a greater likelihood they will develop chronic respiratory diseases later in life.

Developing nations are most at risk of exposure to air pollution. A 2014 study from WHO found that, in these nations, 98 percent of cities with more than 100,000 people do not have access to safe air conditions. Delhi, India, is estimated to be the world's most polluted city.

"A polluted environment is a deadly one—particularly for young children," said Margaret Chan, WHO's director-general, in a press release. "Their developing organs and immune systems, and smaller bodies and airways, make them especially vulnerable to dirty air and water."

Women who come in contact with unsafe environmental conditions during pregnancy also have a greater likelihood of delivering premature babies. The report found that 270,000 children die within their first month of life from exposure to preventable environmental hazards such as unsafe air and water.

Further, children are increasingly at risk from the improper disposal of electronic devices, which can result in toxic chemicals seeping into the environment. Toxins like lead, arsenic, and other dangerous materials can impede mental development and increase rates of cancer.

The amount of improperly disposed waste is estimated to increase by 19 percent by 2018, totaling more than 50 million metric tons.

WHO made several recommendations for improving living conditions for children, including more stringent waste regulations for industries, removing toxic materials (such as lead paint) from building materials, reducing the amount of pesticides used in agriculture, and improving access to clean air and water.

"Investing in the removal of environmental risks to health, such as improving water quality or using cleaner fuels, will result in massive health benefits," said Maria Neira, WHO's director of the Department of Public Health, Environmental and Social Determinants of Health.

The UN's Sustainable Development Goals program is currently working with developing nations to improve access to basic services. The goal is an end to preventable deaths of children under five by 2030.