Before residential use was restricted in the US, data from 1999 to 2000 in the national NHANES study detected the metabolite TCPy in 91% of human urine samples tested. In samples collected between 2007 and 2009 from families living in Northern California, TCPy was found in 98.7% of floor wipes tested and in 65% of urine samples tested. For both children and adults, the average concentrations of TCPy in urine were lower in the later study. A study looking at pregnant women living in an agricultural community in California's Salinas Valley in 2004 showed that 76% of the pregnant women had detectable levels of TCPy. A 2008 study found dramatic drops in the urinary levels of chlorpyrifos metabolites when children in the general population switched from conventional to organic diets.