Intense sunlight, sparse population and a lower median income may all help explain why New Mexico has fewer problems with pharmaceutical residues in drinking water than other states.

But the state's Environment Department wants to keep tabs on surface water to make sure drugs don't become a water quality problem.

The state tested sites around the state from 2000 to 2002 for drug residues, but not antibiotics, focusing on areas with higher populations or known groundwater contamination. Water below wastewater treatment plants like Santa Fe's, which empty into rivers, was tested. Water at some public water systems and private domestic wells also was tested.

National studies indicate 30 percent to 60 percent of the antibiotics, painkillers, antidepressants and hormones people take are excreted into wastewater.

Low-levels of drug residues were found around the New Mexico sites, but varied by type, according to the state's report. Samples taken downstream of Santa Fe's water treatment plant contained residues of the antidepressant amitriptyline, found in Elavil. Amitriptyline residue was also found in a sample taken at the Rio Grande Buckman Crossing, near the city's planned direct river diversion project.

Residue from the anti-convulsant phenytoin (Dilantin) was detected in a sample tested where water from the Española wastewater treatment plant empties into the Rio Grande.

"Drug residues were not detected in the Rio Grande at Pilar, Cochiti Lake, Bernalillo, Paseo del Norte bridge, Belen, Bernardo, San Antonio, or at Elephant Butte Lake. Caffeine and estrone, a type of estrogen, were detected in the Albuquerque South Valley, downstream from the municipal sewage effluent," according to the report.

In the San Juan watershed, the San Juan River at Bloomfield provided the only sample that contained a detectable drug residue, the synthetic estrogen hormone ethynyl estradiol, used in birth control pills.

No drug residues were found in groundwater samples from private domestic wells in La Cieneguilla nor in seven other areas in the state which had previously reported elevated nitrate levels in municipal sewage treatment plant discharges.

"The one thing obvious to us is we don't have the magnitude of pharmaceutical residues that have been found in Germany and parts of the U.S.," said Dennis McQuillan, remediation manager for the Groundwater Bureau of the state Environment Department.

He said the state's sparse population means fewer people excreting drugs. The state's lower income levels might mean "our people are not as medicated," McQuillan said. "They don't have the quantity of medicine and quality of health care as more affluent people."

Another factor in preventing drug residues in New Mexico's water is intense sunlight. "That definitely looks like it plays a role in the rapid reduction of any pharmaceutical residues," McQuillan said.

McQuillan said the samples were a snapshot in time of the water quality at the sites and not a comprehensive look. "These were one-time grabs," he said. "If I had gone back a day or week later, the results might have been very different."

He said the state would like to gather new data on drug residues in the state's waters.

There are no set limits for pharmaceuticals under the Safe Drinking Water Act or the State of New Mexico Drinking Water Regulations, according to Mike Huber of the Environment Department's Drinking Water Bureau. "They are unregulated substances," he said.

Gary Martinez, head of Santa Fe's municipal water division, said the department hasn't tested the city's water for drug residues. "We really don't have a supply that would be tainted," he said.

Currently the city relies on two municipal reservoirs in the mountains east of Santa Fe and groundwater from wells. But he said when the city finishes a direct-diversion project on the Rio Grande and begins to use water from the river, it will need to track pharmaceutical and antibiotic levels which might wash down from upriver towns. He said the treatment plant for the Buckman Direct Diversion project water will have extra barriers like an ozonator and a special membrane to help prevent contaminants from entering the drinking water supply.

Contact Staci Matlock at 986-3055 or smatlock@sfnewmexican.com.