Unsanitary and polluted environments can lead to fatal cases of diarrhoea, malaria and pneumonia which kill 1.7 million children a year, the WHO has reported. The UN agency said the most common causes are preventable.The report "Inheriting a sustainable world: Atlas on children`s health and the environment" released on Monday by the the United Nations public health arm noted that some 25 percent of all global deaths of children under five were due to unhealthy or polluted environments. More than 90 percent of the world`s population is thought to breathe air that violates quality guidelines set by the World Health Organization (WHO), the report noted."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."UNICEF reported last year that two million children were breathing bad air.Increased health risksThe report noted that harmful exposure can start in the womb and then continue if infants and toddlers are exposed to indoor and outdoor air pollution and second-hand smoke."This increases their childhood risk of pneumonia as well as their lifelong risk of chronic respiratory diseases such as asthma. Air pollution also increases the lifelong risk of heart disease, stroke and cancer," the report went on.In households without access to safe water and sanitation or that are polluted with smoke from unclean fuels such as coal or dung for cooking and heating, children are at higher risk of diarrhoea and pneumonia, the report continued.Children are also exposed to harmful chemicals through food, water, air and products around them, it said."Investing in the removal of environmental risks to health, such as improving water quality or using cleaner fuels, will result in massive health benefits," Maria Neira, a WHO expert on public health, said.Top environmental causes of death among children under five:The top causes were listed as respiratory infections with 570,000 deaths in children under 5 years linked to indoor and outdoor air pollution and secondhand smoke; diarrhea with 361,000 deaths in children under 5 linked to poor access to clean water, sanitation and hygiene.The WHO reported 270,000 deaths in children under 1 month could be prevented by access to clean water, sanitation and hygiene in health facilities, and by reducing air pollution.The agency also reported that 200,000 deaths caused by malaria in children under 5 could be prevented by environmental improvements, including reducing mosquito breeding sites or covering drinking water storage.There were also 200,000 deaths among children under 5 linked to their environments, including poisonings, falls and drowning - cited as "unintentional injuries."Source: Deutsche Welle