River water samples were collected once a month at the same
location between 8 am and 11 am in a sterile 1 l Schott glass bottle
from the river source at the same point that irrigation water for the
produce is extracted. Water was obtained from areas of fast flow at adepth half that of the total in order to avoid debris and collecting
exclusively surface water. Samples were transported on ice and
analyzed within 2 h.