Pesticides, Soil Life & Infiltration Rates
Sustainability for all the places between the buildings.

This is a page reprinted with permission from Karen Sands, who summarized her findings on the the impact of pesticides on soil life and hydrology on EPA's listserv called "npsinfo".

Her conclusion is at the bottom of the page, but I'm reprinting it here:

The elevator speech I take away from this: Pesticides adversely affect soil health, and that in turn likely reduces stormwater infiltration rates. While many experts agree that pesticides decrease stormwater infiltration rates, this is an area of research that should be investigated further and quantified.


From: "Karen Sands" <>
To: "NPS Information Exchange" <>
Sent: Tuesday, May 15, 2012 9:48:14 AM
Subject: [npsinfo] Follow up from last month

Several of you asked for this, so here goes…

I sent the following question to the US Environmental Protection Agency’s (EPA) Non-point Source Information Exchange [npsinfo] on April 17, 2012:

“Water quality and human health impacts aside, has anyone come across studies related to the effects of pesticide use on macrobiology in soils and, in turn, its potentially detrimental impact on stormwater infiltration? I’m specifically interested to know if pesticide use on lawns has been linked to decreased stormwater infiltration in studies…and if that detrimental impact has been quantified in the literature.“

As a result, I received responses from eight academic and stormwater professionals (I’ve protected everyone’s anonymity below). None called my question into question, and most rather said that pesticide application would decrease stormwater infiltration and that they are interested in the topic. This is a typical response: “…the use of pesticides destroys soil structure and that will always reduce storm water infiltration. It is almost too obvious for studies (Karen’s emphasis added), and I don't mean that in a pejorative way!” Another respondent who is heading up a sustainable landscape initiative said that if there is a lack of research out there then perhaps he has some basis for conducting such a study.

Another respondent said: “I don’t have any specific literature citation I can recommend but there is no doubt in my mind that pesticide use on lawns does indirectly reduce stormwater infiltration because those pesticides are disrupting one or more components of the soil ecosystem; components that help “build” soil and increase infiltration. “

Another respondent said: “I don’t have any answers but this is a great question and I look forward to replies. It makes sense that pesticides could damage soil microbes and ecology and this could affect infiltration rates, as well as other aspects of the processes that improve water quality as it moves through the soil. “

And, finally, a gardening book author said “The loss of the fungi and bacteria at the bottom of the soil food web, micro and macro arthropods and finally worms, always results in compaction and that in turn results in decreased infiltration.”

I also receive several URL’s with good information, but most of it focusing on water quality impacts of pesticides rather than on soil health/water quantity.. And, unfortunately, no respondents had data specifically on the question of reduced infiltration rates associated with pesticide use on lawns.

One doctoral dissertation I was sent provides some insight, but it’s much more about water quality than about the effects of pesticides on the water quality holding capabilities of turf: "THE HYDROLOGICAL FATE OF NUTRIENTS AND PESTICIDES IN THE URBAN LANDSCAPE IN REPONSE TO MANAGEMENT AND LAWN SPECIES” by Mark Ryan Slavens, Ph.D., Cornell University 2010 . Select insights from this dissertation include:

· “The applications of fertilizers and pesticides to home lawns may contribute to the deterioration of ground and surface water quality. Loss of nutrients and pesticides to ground and surface water can be detrimental for human consumption, reduce recreational usage, and negatively impact aquatic organisms.”

· “A field study was initiated to examine the effect fertilizer and pesticide applications can have on the concentrations and mass loss of nutrients and pesticides in leachate and runoff.” I’ve left a LOT of details out, but in general it found:

o “Nitrate contributions in leachate reflected the overall largest potential loss from the landscape.

o Pesticide applications could pose a risk to water quality, but the risk to off-site surface water contamination appears to be much more prevalent.

o Over-time, levels of pesticides in runoff were reduced; however during establishment, concentrations of 2,4-D and Mecoprop were greater than 2800 and 1600 μg L-1, respectively, which could negatively impact aquatic organisms.

o Most often the highest concentrations of pesticides in runoff and leachate occur during the first rain event following application and concentrations diminish with time. In a simulated rainfall experiment, Smith and Bridges (1996) found that detectable concentrations of mecoprop in a greenhouse lysimeters study only occurred in the leachate for 21d after treatments were applied. For all herbicides [2, 4-D(2,4-dichlorophenoxyacetic acid); mecoprop [2-(4-Chloro-2-methylphenoxy)propionic acid]; dicamba(3,6-dichloro-2-methoxybenzoic acid)], the total analyte transported from the greenhouse lysimeters was less than 1.0% of the herbicide applied. The highest concentrations of herbicides found in leachate did not exceed 6 μg L-1 and the concentrations of dicamba in the leachate from bentgrass did not exceed the minimum detectable level (1 μg L-1). The highest concentrations of 2, 4-D transported from lysimeters containing bentgrass ranged from 3.5 and 5.8 μg L-1 dependent on formulation. The MCL of 2, 4-D of 70 μg L-1 was at least 10 times above the highest 117 concentration determined for the herbicides transported from the lysimeters studies.

o The hydrological mobility of pesticides applied to the landscape is concerning for aquatic, vegetative and human health. Differing chemistries of pesticides along with cultural practices applied to the landscape are factors that can impact the transport of herbicides to surface and groundwater from application sites.”

Regarding water quality impacts, another respondent mentioned that “We find chlordane and dieldrin (applied into the ground around and beneath foundations as a termiticide) in stream and estuary sediments, and some aquatic species, even though these compounds were banned years ago by EPA. They are being transmitted through the soil by infiltration of rain and thence by seepage into streams/groundwater. “

The elevator speech I take away from this: Pesticides adversely affect soil health, and that in turn likely reduces stormwater infiltration rates. While many experts agree that pesticides decrease stormwater infiltration rates, this is an area of research that should be investigated further and quantified.

Karen L. Sands, AICP
Manager of Sustainability
Milwaukee Metropolitan Sewerage District
(414) 225-2123

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Updated 2 Jun 2010