Road salt for deicing may be causing elevated levels of chloride, a component of salt, in many urban streams and groundwater across the northern U.S., according to a new government study. Other chloride sources include wastewater treatment, septic systems and farming operations.

Chloride levels above the recommended federal criteria set to protect aquatic life were found in more than 40 percent of urban streams tested, according to a study released last week by the U.S. Geological Survey (USGS). Elevated chloride can inhibit plant growth, impair aquatic life reproduction and reduce the diversity of organisms in streams.

Chloride levels in drinking-water wells were lower, with elevated levels found in fewer than 2 percent of drinking-water wells sampled in the USGS study. The report points out that increases in chloride levels in streams during the last two decades are consistent with the overall increase in use of salt for deicing and the expansion of road networks and parking lots that require deicing. "Safe transportation is a top priority of state and local officials when they use road salt. And clearly salt is an effective deicer that prevents accidents, saves lives and reduces property losses," said Matthew Larsen, USGS associate director for water. "These findings are not surprising, but rather remind us of the unintended consequences that salt use for deicing may have on our waters. Transportation officials continue to implement innovative alternatives that reduce salt use without compromising safety."

The study examined chloride concentrations in the northern U.S. covering parts of 19 states, including 1,329 wells and 100 streams. View the entire "Chloride in Groundwater and Surface Water in Areas Underlain by the Glacial Aquifer System, Northern United States" study.

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