Mercury contaminates fish and, when ingested by pregnant or nursing women, can cause neurological damage.

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Third, it would need to have a biological effect when ingested.

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The group's counsel, David Wilby QC, has told Mr Justice Akenhead that the disabilities were caused early on in their foetal development when their mothers ingested or inhaled an "atmospheric soup of toxic materials" from the redevelopment.

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Experts say the effects are only more serious if the substance is ingested, when it can cause damage to lungs and the digestive system, and could prove fatal in some cases.

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These materials harm people mainly when they are inhaled or ingested, which is why people in danger zones are often wearing masks and why people have been advised to stay inside and wear long sleeves.

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When chemical preservatives and color enhancers are ingested, they cause the body to produce nitrosamines which cause cancer of the liver, stomach, brain, bladder, kidneys and several other organs.

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"There is the problem of plastic bags and balloons which have been ingested by leatherback turtles off Cardigan Bay when mistaken for jelly fish, " said Ms Bell.

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The disease gets into the body when people drink contaminated water, which contains water fleas that have ingested Guinea worm larvae.

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