Arsenic and boron were the trace elements that most frequently occurred at high concentrations. Fumigants (pesticides) were detected at high concentrations in 3% of the primary aquifers. Herbicides and insecticides were detected at low concentrations.
Vanadium and boron were detected at high and moderate concentrations in this area. High concentrations for these constituents were detected almost exclusively in samples collected in the Temecula Valley study area.
Even though lead usage has declined due to environmental awareness and regulation, several human sources of lead continue to affect birds. Hunting ammunition and fishing gear are ingested by the birds, with toxic effects.