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Hundreds of thousands of Costa Ricans in the Central Valley could be drinking water heavily laced with cancer and DNA mutation-causing pollutants, probably from septic tanks and coffee plantations.

Three long-term studies of underground water in the Virilla River basin in the western Central Valley revealed levels of nitrates and other contaminants in drinking water approaching or exceeding maximum limits recommended by health authorities.

Investigators of the Universidad Nacional (UNA) in Heredia, north of San José, periodically monitored 11 wells and nine springs in the basin from 1990-2002.

The aquifers underlying the territory serve more than a million residents, and 20 per cent of the water sources studied contained dangerous levels of nitrates on at least one occasion. And the levels are rising, the investigators discovered.

"If measures are not taken, in a few years this water will not be able to be used for human consumption," said Jenny Reynolds, head of UNA's Environmental Hydrology Center.

UNA investigators this week released the results of the studies, funded in part by the International Atomic Energy Agency and the Costa Rica-United States of America Foundation for Cooperation (CR-USA).

The Virilla River basin is sprawled over an area of nearly 1,000 square kilometres, which is two per cent of Costa Rica 's total land, but home to 43 per cent of the country's population. UNA investigators point the finger at this concentration of humanity, its constellations of industries, plantations and rivers of untreated sewage, for contaminating aquifers.

Nitrates, found in sewage and fertilisers, seep into the region's volcanic aquifers from septic tanks and coffee plantations, while harsh chemicals in industrial waste and spills, called volatile organic compounds, leak into water sources and wreak unpredictable havoc on the drinkers' health.

“Unfortunately, [the pollution of underground water] is a slow process, which means when the contaminants are detected, it is hard to reverse the process,” Reynolds said.

Volatile organic compounds are cancer- and DNA mutation-causing at low levels, Reynolds said. The degree to which health is affected is uncertain, however, because tests on humans are not easily conducted.

Paints, glues, solvents such as perchloroethylene — the main solvent used in dry cleaning — paint and lacquer thinners, insect repellents, air fresheners, hobby supplies, wood preservatives, aerosols, degreasers and automotive products are among those that release volatile compounds.

Their effects on health vary from being highly toxic to not at all, depending on the compound and the level and length of exposure, according to the U.S. National Library of Medicine.

Long-term exposure can cause liver, kidney and central nervous system damage. Short-term exposure can cause a list of symptoms from headaches and skin reactions, to nausea and forgetfulness.

The compounds are easily washed into groundwater sources, UNA scientists report, such that even a small spill can pollute “millions of litres of subterranean water.”

Three times between 1999-2004, investigators tested 32 sites in the Virilla River basin for the compounds. The water was drawn from wells and springs fed by the upper and lower Colima aquifers and the Barva aquifer, one of the most important — and closest to the surface — drinking water sources in the region. Of those, nine were polluted with volatile compounds.

"In general, the concentrations do not surpass maximum levels permitted, but the fact that they are present indicates that there is an active process of contamination," the investigators report.

Reynolds highlighted one of the region's cantons, Belén, as the most highly polluted of the area, suggesting that its recent population explosion and corresponding industrial development could be the culprit.

More than 20,000 people are squeezed onto Belén's 12 Km2, which they share with 70 industrial establishments, the investigators report.

"I can't confirm the causes [of water pollution in Belén], but we can assume it's industry," Reynolds said.

An important water source in the river basin is the spring Ojo de Agua, located in the swimming and recreational area of the same name. The investigators found it has “relatively high concentrations of volatile compounds.”

They mention the spring and the discovery of contaminants in two wells drawn from the Colima aquifers, which are much deeper than Barva, as "worrisome" because it appears the soil and rock layers above the water are not sufficient protection.

"The management of water in the Central Valley is not sustainable — that means we can't guarantee clean water for our children or grandchildren," Reynolds said.

The Barva aquifer has been under UNA's microscope since 2001. The study aimed to enlighten city planners to the dimensions, characteristics and vulnerabilities of this shallow-set aquifer that supplies water to 500,000 people in the Central Valley.

It is beneath some of the country's heaviest population growth regions, where the concrete and pavement block some of the aquifer's recharge zones, making rain and groundwater run off rather than seep in.

The investigators call for a subterranean water-management plan based on the results of their studies. They recommend that springs and wells be zoned off and regulated to protect their purity, septic tanks be phased out of use, replaced with sewage pipes and waste-water treatment plants, and crop fertilisation techniques be made more efficient so as not to allow so many nitrates into the water supply.

They have begun to mark off areas around wells and springs that should be regulated to protect the water.


Reprinted with permission from The Tico Times (

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