A state of emergency has been declared in the city of Flint, Michigan, due to dangerously high levels of lead being discovered in the blood of local children. The culprit appears to be a change in the city’s main water source, and a number of residents have filed a class-action federal lawsuit against the state, the city, and several officials for exposing their families to highly toxic drinking water.

"For more than 18 months, state and local government officials ignored irrefutable evidence that the water pumped from the Flint River exposed [city residents] to extreme toxicity," says the lawsuit. "The deliberately false denials about the safety of the Flint River water was as deadly as it was arrogant."

So what can lead exposure actually do to the body? A whole lot, as it turns out, and very quickly too. Yang Wang reports forThe Washington Post that parents in Flint have been turning up at their local GPs for months, concerned that their children had been poisoned.

According to the World Health Organisation (WHO), when it comes to lead poisoning, the onset of learning disabilities and changes in behaviour are just the beginning. While exposure in adults can cause kidney damage and high blood pressure, young children are especially vulnerable, because they can absorb up to five times as much lead from the same source as adults. Once inside the body lead is distributed to organs such as the brain, kidneys, liver and bones, and accumulates.

"In particular, lead affects children’s brain development resulting in reduced intelligence quotient (IQ), behavioural changes such as shortening of attention span and increased antisocial behaviour, and reduced educational attainment," says the WHO. "Lead exposure also causes anaemia, hypertension, renal impairment, immunotoxicity and toxicity to the reproductive organs. The neurological and behavioural effects of lead are believed to be irreversible."

The lawsuit also mentions hair loss and skin lesions as effects reported by the exposed residents.

A report from the Hurley Medical Centre in Flint has shown that since April 2014, the number of local children with above-average levels of lead in their blood has almost doubled. In some places, 15 percent of the children tested have shown dangerous levels of lead in their blood. This has gotten everyone very, very worried.

That 2014 date is important - it’s when the city switched its main water source from the Detroit river system to the local Flint River, and that decision has since been blamed for the health crisis.

What's perhaps most troubling is that residents have been complaining about the quality of the water ever since the change was put in place almost two years ago. The fact that Flint Mayor Karen Weaver declared a state of emergency on Tuesday 15 December to get the attention and assistance of federal officials didn’t come as a surprise - it was a long time coming for the locals.

"Almost immediately after the city started drawing from the Flint River in April 2014, residents began complaining about the water, which they said was cloudy in appearance and emitted a foul odour," Wang reports.

"Since then, complications from the water coming from the Flint River have only piled up. Although city and state officials initially denied that the water was unsafe, the state issued a notice informing Flint residents that their water contained unlawful levels of trihalomethanes, a chlorine byproduct linked to cancer and other diseases."

Locals were advised by the city that children, the elderly, pregnant women, and anyone with a weakened immune system should seek advice from their doctor about whether they should be drinking the water. In the face of all the evidence that the water was dangerous to their health, the Flint residents had but two choices: live off expensive bottled water indefinitely, or take a risk and drink the tap water. Understandably, they've been protesting and petitioning this for months.

As recently as this October, Flint officials finally caved and switched the main water supply back to the Detroit river system. Their original plan had been to keep using the Flint River system till some time in 2016, so the state could construct a new pipeline connecting the city to Lake Huron in Detroit. The plan was supposed to save them millions of dollars when complete.

With a state of emergency now in place, officials are in damage control. According to Arielle Duhaime-Ross at The Verge, the Federal Emergency Management Agency (FEMA) has sent 28,000 litres of bottled water to a local food bank.

Michigan governor Rick Snyder - who many hold responsible for the crisis - has financed the multi-million-dollar switch back to the Detroit river system. Flint is offering the locals free water testing and free water filters, and is assessing homes fitted with lead piping that could be making things even worse.

But even now, there could be some areas in the city where the water is still unsafe to drink if left unfiltered, and there’s no telling what the long-term effects of the exposure will be. As The Washington Post reports: "[Flint Mayor, Karen] Weaver thinks that these health consequences will lead to a greater need for special education and mental health services, as well as developments in the juvenile justice system."