Decreased risk to humans with dropping pesticide levels in natural water sources

Pesticides, herbicides and fungicides enter our natural water systems from runoff from home and agricultural use.  Once these intoxicants enter our rivers and streams they pose a hazard not only to humans, but also to wildlife.  From 1992 to 2011 over half a billion pounds of herbicides, insecticides, and fungicides were used annually on crops and to protect from insect-borne disease (1). The U.S. Geological Survey ran a 20 year survey of rivers and streams to track changes in the prevalence of these contaminants and published a study with the findings in the journal Environmental Science & Technology, and an article in the New York Times discussed these findings.

The New York Times article Pesticide Levels in Waterways Have Dropped, Reducing the Risks to Humans highlights the findings of the article Pesticides in U.S. Streams and Rivers:  Occurrence and Trends during 1992-2011 published in the journal Environmental Science &Technology.  The study examined the prevalence of a large number of pesticides at 200 sites in rivers and streams over a period of 20 years, starting in 1992 and continuing to 2011 for the the presence of these compounds as well as if the concentrations exceeded the aquatic-life or human-health benchmarks.  The sites were located in a mix of different land use areas, including agricultural, urban, and mixed.  The scientists found that the proportions of steams that exceeded the aquatic-life benchmark for at least one pesticide were similar between the two decades for agricultural and mixed-land-use streams, but increased in urban streams.  While the aquatic-life benchmarks were exceeded at about the same rate from 1992-2001 and 2002-2011 the human-health benchmarks were only exceed in one agricultural stream during 2002-2011.

Figure 1. The national monitoring network for pesticides in streams and rivers included 182 sites during 1992-2001 and 125 sites during 2002-2011, with 96 of the sites comon to both decades.  Concentration trends were assessed for 39 major rivers with mixed land use and 27 urban streams.  From Pesticides in U.S. Streams and Rivers: Occurrence and Trends during 1992-2011

The study attributed this decrease to a decrease in use of these compounds due to voluntary discontinuation, as well substitutions by new compounds. The new compounds were to be stronger so they can be used in smaller amounts which decreases how much can runoff into rivers and streams.  The New York Times article includes a quote from one of the study's scientists which also attributes some of decreases to the success of regulatory changes "'It's very clear in the data that regulatory changes in use do affect what you see in the streams"' said Wes Stone, a hydrologist with the Geological Survey...".  

Figure 4. Proportion of streams with one or more pesticides that exceeded a chronic aquatic-life benchmark was very similar between 1992 and 2001 and 2002-2011 for agricultural and mixed-land-use streams, but much greater during 2002-2011 for urban streams.

The study also highlighted the fate of seven pesticides that were frequently found to exceed the aquatic-life benchmarks to highlight how changes in concentrations and usage of a compound can lead to many different trends. For most of these compounds they found decreasing concentrations, but one found at an increasing rate and concentration was Fipronil, the main ingredient in many cat and dog flea and tick prevention medications.  Fipronil usage in the United States began in the late 1990s as a replacement for organophosphate insecticides.  It was found in 70% of urban streams, and 20% of agricultural and mixed-land-use streams between 2002 and 2011.

While the 20 year study shows some decreases in amount of pesticide, herbicide and fungicide usage in rivers and streams, this study only monitored less than half of the number of these compounds used in agriculture in the U.S.  This limited study was due to both limitations in analytical methods for analysis as well as limitations in funding.  The scientists of this study have stated that the result of this limited scope of study is that the risks to wildlife are probably higher that the findings of this study show.

The NY Times article did a good job of describing the results of the U.S. Geological Survey study.  It highlighted the main findings of the study, and included some of the limitations.  I also liked that it included a quote from one of the researchers discussing the successes of regulatory work.  I thought that this was a strong message to the readers about a positive outcome of regulatory work for environmental and human health.  The NY Times article was a bit strong in a few of the statements it makes, for example "The results nevertheless documented a striking decline in danger to humans from pesticide pollution", when the Environmental Science and Technology article states that the proportion of streams with at least one pesticide that exceeded the aquatic-life benchmark were very similar between the two decades.  This bold statement by the New York Times article makes it appear that the number of pesticides in the water is less dangerous than it may actually be.  Despite some of the overly strong statements, I thought that it was a strong article and stayed true to the Environmental Sciences &Technology article, therefore I give it a 7 out of 10.

Journal Article:
(1) http://pubs.acs.org/doi/pdf/10.1021/es5025367

New York Times Article:
http://www.nytimes.com/2014/09/12/us/pesticide-levels-in-waterways-have-dropped-reducing-the-risks-to-humans.html?_r=0