So Dr Orantes thinks a major cause of their kidney damage is the toxic chemicals - pesticides and herbicides - that are routinely used here in agriculture.
"These chemicals are banned in the United States, Europe and Canada, and they're used here, without any protection, and in large amounts that are very concerning," he says.
But he's not ready to rule out other possible causes. For instance, the overuse of painkillers can damage the kidneys, and so can drinking too much alcohol. Both are major problems here, he says....
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