City rain run-off poses threat to coastal water users

03/31/04

Rainwater running off city roofs and streets poses health risks to surfers and others who spend time in coastal waters, according to a new study.

Spending more time in the surf increased risk of fever, stomach pain, vomiting, diarrhea, skin infection, eye redness and other symptoms, according to the report in the American Journal of Public Health.

"These potential health risks warrant greater public health surveillance, as well as greater efforts to reduce pollutants discharged onto public beaches," say Ryan Dwight, Ph.D., and Dean B. Baker, M.D., M.P.H., of the University of California, Irvine, and colleagues.

The researchers interviewed surfers in 1998 and 1999 at two California beaches. One was North Orange County, whose watershed is one of the most developed in the world and which produces highly polluted runoff water. The other was in rural Santa Cruz County, which is farther north, less urbanized and less polluted.

"Surfers were selected as the study population because of their regular exposure to coastal waters," Baker says. In all, they interviewed 1,873 participants, asking about any illness symptoms they had experienced over the previous three months.

They also compared rainfall at the two beaches in each year and used local health department data to get coliform bacteria counts, a water pollution measure. Santa Cruz County had higher total rainfall each year compared to North Orange County, yet the latter had higher water coliform counts.

As it happened, California experienced record high precipitation in the winter of 1998, thanks to the El Niņo effect. Surfers in North Orange County that year reported almost twice as many symptoms and higher rates of every symptom than those in Santa Cruz County.

By contrast, the winter of 1999 saw the opposite climate pattern, called the La Niņa effect, which caused record low precipitation. Drier conditions that year produced only slightly more symptoms in North Orange County compared to Santa Cruz.

That the coastal water was the key factor affecting the surfers' health was reinforced by the time spent out on the waves. Symptoms risk increased by about 10 percent for every additional 2.5 hours the surfers spent in the water per week.

"Research on the health consequences of urban runoff represents a relatively new area of investigation," says Baker. Most previous work focused on single episodes of sewage contamination, but this study looked at more generalized runoff.

Source: Eurekalert & others

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