Chemicals from fertilizer, household products impact Bay Area water

07/08/10 Matthew Cimitile
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Large algae blooms can be the result of excessive nitrogen and phosphorus running off of agricultural fields and lawns into waterways. They deplete oxygen and harm fish, shrimp and other aquatic life. Pinellas and Sarasota Counties have outlawed fertilizers on residential lawns during the summer because of the harmful effect excessive fertilizer use has on the marine environment. Sierra Club representative Phil Compton says Hillsborough must follow suit.

“Scientists tell us as much as 79% of the nitrogen from local lakes has been proven to come from fertilizer runoff from our lawns. Most of our lakes and rivers are sick in Hillsborough County. They are officially impaired from nitrogen and phosphorus nutrient pollution from lawn fertilizer. This excess nitrogen and phosphorus has led to really significant harmful algae blooms, we have had dead zones, we have had significant declines in wildlife and wildlife habitat, it hurts our drinking water supply and it is really detrimental to our whole tourism-based economy and our quality of life.”

Compton says the first step to reduce such contaminants in the Bay area will be for Hillsborough County to continue the precedent set by Sarasota and Pinellas and ban fertilizer use from June through September.

In the Tampa Bay area, groundwater is also affected by fertilizer use. That’s because the water table is so shallow and there are many sinkholes. U.S. Geological Survey hydrologist Patty Metz says because Tampa’s surface waters and groundwater are so interconnected, chemical compounds coming from households and lawns find their way into aquifers.

“Underlying Tampa Bay we have a limestone aquifer where we get about 60% of our drinking water supplies in the northern Tampa Bay area. This limestone is overlain by sand and clay layers and for most part acts as a filtering system for surface contaminants. But in areas that are prone to sinkhole development, breaks in the clay form and surface contaminants can move more easily down through these breaks. We have found from our studies that surface contaminants are more likely to be detected in these sinkhole prone areas. In these areas where compounds are applied to the surface such as the pesticides and fertilizers, these contaminants can move downward to the underlying aquifer by rainwater and overland flow infiltration.”

Metz says the USGS randomly sampled 30 groundwater wells in Tampa Bay and found increases in nitrogen and small concentrations of pesticides and waste-water compounds.

“From our study we found compounds were detected at very low levels, and they were below the maximum contaminant levels, or MCLs, which are set by EPA. They are unlikely to be of potential human health concern. These contaminant levels are set mandatory levels for drinking water contaminants, but we found 15 of our compounds did not have any standards and we call these unregulated compounds, and there are thousands of these unregulated compounds and human health implications aren’t known because there’s insufficient toxicity information regarding these compounds.”

Groundwater concentrations of these compounds were higher near population centers. Metz says the most common contaminates were chloroform, a volatile organic compound formed from the chlorination of drinking water, and atrazine, an herbicide that has recently been shown to affect the reproduction of fish and frogs.

“It’s a common weed killer and it also has the breakdown product deethylatrazine. We found it in the groundwater system in the northern Tampa Bay area where concentrations were highest in the urban land use areas where lawn care products are most extensively used. And a number of reasons for the high detections for atrazine and the deethylatrazine is the high mobility in sandy soils, its widespread use -in the United States it is the most widely used herbicide - and its persistence in groundwater. Atrazine can persist in soils up to 100 days but once it gets into the groundwater atrazine can last 6 years, where deethylatrazine can persist for 25 years.”

Atrazine is banned in Europe because of its persistence in groundwater. The Sierra Club’s Compton stresses that governments and the public can do many things to reduce runoff and chemical compounds entering both surface water and groundwater.

“The key to making this work, the key to having green and healthy lawns and clean, clear, healthy waterways is to require all nitrogen fertilizer sold October to May be slow release type. That means half the prills, half the little bits of fertilizer, are quick release in a bag of fertilizer and half slow release. And these high quality products are going to last for 3 to 6 months. In that way you can apply it in April and May on your lawn and this time of year, in the summertime, you don’t have to do a thing. It is just a matter of using the right kind of fertilizer at the right time of the year. Another thing people can do though is using the right plant in the right place ... using Florida native plants, especially along waterways that don’t require fertilizer, really is a way that we can help.”

Recent studies are uncovering chemical compounds from lawn applications and personal-care products draining into groundwater sources.

The silent flow of fertilizers and other nutrients down the Mississippi River for decades has resulted in a dead zone in the Gulf of Mexico, that NOAA predicts stretches for close to 9,000 square miles.

Hillsborough County Commissioners will vote on the fertilizer ban ordinance during their Environmental Protection Commission meeting on July 15.

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