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    Climate change could poison Earth’s lakes and rivers with toxic pathogens, experts warn

    Climate change is poisoning the planet’s water, it has been claimed.
    A new study found increasing organic runoff, known as ‘browning’ the water, may be reducing the penetration of pathogen-killing ultraviolet (UV) sunlight.The find could mean an explosion in the number of  waterborne pathogens, which already cause 19 million people to become ill each year.
    The new study in the journal Scientific Reports, led by Miami University in Ohio, analyzed water samples.
    Scientists have already measured an increase in ‘browning’ of the world’s waters, a phenomenon caused by more organic matter washing in from the surrounding land. 
    Not only does an increase in dissolved organic matter make it more difficult for sunlight to disinfect bodies of water, it also makes it more difficult for water treatment plants to work effectively, said lead author Craig Williamson, a Miami University ecologist. 
    In the United States, 12 to 19 million people already become ill from waterborne pathogens annually.
    ‘Water clarity is dropping in many regions due to factors such as browning, and this research demonstrates that this change is likely decreasing natural disinfection of potentially harmful pathogens,’ said Kevin Rose of Rensselaer, who gathered much of the data on dissolved organic matter in water samples to assess the potential of UV radiation to kill pathogens.
    The team used samples of water from lakes around the world, from Pennsylvania and Wisconsin, to Chile and New Zealand. 
    Tests determined the amount of dissolved organic matter contained in each sample, and the wavelengths of light – including ultraviolet wavelengths – absorbed by that organic matter.
    The results allowed scientists to quantify the impacts of dissolved organic matter.
    For example, the summertime SIP for one lake in northeastern Pennsylvania – which, along with other regional lakes has undergone significant browning in recent decades – dropped by about half between 1994 and 2015.
    In California’s Lake Tahoe, the SIP in the relatively pristine center of the lake can be as much as 10 times greater than at Tahoe Meeks Bay, an area at lake’s edge that is heavily used by humans and has a much higher level of dissolved organic matter.

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