Evaluation of Pesticide Residues at Schools in Close Proximity to Vineyards in South Africa

One of the major concerns about the use of pesticides in viticulture and agriculture in general is the potential for these chemicals to drift onto neighboring farms that do not wish to use these pesticides, and more importantly, into residential areas where people live, work, and play.  Studies have shown that pesticides sprayed on agricultural fields can drift upwards of 400 to 750 meters away from the spraying area.

Why does it matter if a little bit of residual pesticides make it to a neighborhood, or perhaps even a school yard?  There have been many studies looking at the effects of exposure to environmental toxins on public health, with children in particular being much more sensitive to these effects than their adult counterparts.  Children do not yet have a fully developed immune system, have higher metabolism rates, and are very active outside (or they should be, anyway!), so by nature, they are often more exposed and more sensitive to the effects of pesticide drift than other populations.

Photo by Jeff Vanuga, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSAZ02083.tif) [Public domain], via Wikimedia Commons

Photo by Jeff Vanuga, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSAZ02083.tif) [Public domain], via Wikimedia Commons

Studies in the United States and abroad have found that exposure to pesticides can cause acute illnesses in students and employees at schools, with long-term health implications abound for those exposed to low levels of pesticides on a somewhat regular basis.  Specifically, long-term exposure to low doses of pesticides have been linked to many health problems, including but not limited to neurological problems, endocrine disruption (which has many negative consequences for nearly every function in your body), cancer, or DNA mutations and damage.

The goal of the study presented today was to look at pesticide drift from two vineyards in South Africa that neighbor two schools, specifically to determine if the children at these schools are being exposed to potentially harmful levels of pesticides and how the presence of these pesticides correlate with when they were sprayed at each vineyard.


Air, dust, and grass samples were taken at two different times during the study: once at the beginning (prior to spraying), and once during the spraying season.  The baseline samples were collected over one day, while the second sampling time during the spraying season was carried out over 2 weeks per school (2 schools: 4 weeks total).

Two schools were included in this study, both of which were located next to vineyards and about 5km away from the outskirts of Cape Town, South Africa.  The schools were located approximately 700m apart.  One school was a pre-school for children from age 3 to 6 years, while the other school was a primary school (elementary school) for children from age 6 to 12 years.  The primary school was located about 100m away from the vineyard, while the pre-school was located 30m from the nearest vineyard.  The playground for both of the schools was located only 15m from the nearest vineyard.

Air samples were collected using a device called a Drift Catcher, which has been frequently used in these types of studies.  The drift catcher was placed 30m from the nearest vineyard in the school play areas.  For the baseline samples, the drift catcher was set in location for 24 hours.  For the samples taken during the spray season, the drift catcher was set up between 9am Sunday morning and 12pm Friday afternoon, with samples collected once per week for two weeks at both schools.  Air flow rate, ambient pressure, and temperature were also recorded.

Dust samples were collected using a standard household vacuum cleaner and were collected on the same days as the air samples. Each school was instructed not to perform their usual vacuuming or cleaning regimes, so that all of the dust samples went into analysis (and not the trash).  Rugs are carpeted surfaces were vacuumed three times at each sampling date.

Photo By D. Sharon Pruitt from Hill Air Force Base, Utah, USA [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Photo By D. Sharon Pruitt from Hill Air Force Base, Utah, USA [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Grass samples were collected on the same days as the air and dust samples.  The grass in the two play areas was cut using a standard lawn mower, with all cuttings collected for analysis.  Pesticide residues were analyzed for each sample in the laboratory using a kit with the ability to detect up to 126 different pesticides.  Chemical compounds were identified using gas chromatography-mass spectrometry and flame photometry.

For controls, samples from a site far away from agricultural fields were collected and analyzed.

Spraying schedules were collected from the two area vineyards, as well as information regarding the weather conditions throughout the duration of the study.


  • 14 pesticides were reported to have been sprayed at the vineyards, with 7 of them detectable using the chosen laboratory method.
  • 5 pesticides were detected in the air samples.
    • At baseline, endosulfan was detected.
    • After 1 week of spraying, endosulfan, kresoxim-methyl and boscalid were detected.
    • After 2 weeks of spraying, kresoxim-methyl, penconazole, dimethomorph, and boscalid were detected.
      • Kresoxim-methyl was not on the spray schedule at either vineyard.
  • 5 pesticides were detected in the dust samples.
    • At baseline, chlorpyrifos, cypermethrin, permethrin, pyriproxyfen, and endosulfan were detected.
    • During the spraying period, chlorpyrifos, cypermethrin, permethrin, pyriproxyfen, endosulfan, kresoxim-methyl, dimethomorph, and bromopropylate were detected.
    • Concentrations for most compounds were similar throughout the spray period, however, permethrin concentrations significantly decreased from 3.21mg/kg at baseline to 1.15mg/kg at week 1 of the spraying period.
    • It took about 5 weeks after the spraying of bromopropylate to be detected at the schools.
    • Chlorpyrifos, pyriproxyfen, cypermethrin, permethrin, and kresoxim-methyl were detected at the schools, however none of them were on the spraying schedule at either vineyard.
    • Folpan, quinoxyfen, sulphur, and alkarylpolyxyethylene were reported to have been sprayed by one of the vineyards, however they were not detectable in the analysis due to limitations in the detection kit (did not have the ability to recognize those compounds).
  • 3 pesticides were detected in the grass samples.
    • At baseline, only endosulfan was detected.
    • During the spraying period, endosulfan, kresoxim-methyl, and penconazole were detected.
    • Endosulfan had a 100-200% increase in concentration from the baseline to the end of the spraying period.
  • In terms of weather, the best conditions for pesticide drift toward the schools would be a North (N) or North-Westerly (NW) wind.
    • During the first week of the spraying period, 5 out of 6 days had a N or NW wind, though on 4 of those days it rained (potentially decreasing the effect of the drift).
    • During the second week of the spraying period, only 1 day had a N or NW wind, and it also rained on that day.
    • Wind and rain data correlated well with the concentrations of pesticides throughout the study.
  • In control samples, chlorpyrifos, cypermethrin, and permethrin were detected, while no agriculturally used pesticides were detected.

Concluding Thoughts

The results of this study indicate that some pesticides do, in fact, drift from neighboring vineyards to schools and likely other nearby locations, though the concentrations found in this study were generally lower than concentrations found in other studies.  Overall, the weather during this study period was favorable to decreasing pesticide drift (lots of rain and favorable winds), so longer term studies are needed to understand this process further.  Also, perhaps the pesticides weren’t found in as high concentrations as they could have been under more favorable weather conditions, but those residues had to go somewhere.  Did they end up in the water supply?  Where are they if they weren’t found at the playground?

In terms of health implications, the authors noted it is very difficult to determine from this or any study if the levels of pesticides found at the school are high enough to bring about negative health issues, as there are currently no consistent safety levels indicated for these compounds.  While the samples collected were relatively low in concentrations of pesticides compared to other studies, is it low enough to be deemed “safe”?

While acute exposure to low levels of pesticides may not be harmful, what happens when there is long term exposure, such as children playing on the playground every day for 9 or more years (as they would if they attended these schools from age 3 to 12)?  The bioaccumulation of toxins has been widely studied with other chemicals, and occurs when tiny amounts of a chemical collect somewhere in the body at rates faster than the body can get rid of them.  That means, while each exposure may net you very little in terms of absorption into your body, over a longer, or more chronic, exposure time those small concentrations add up to large concentrations, causing a plethora of health problems from neurological damage, reproductive problems, cancer, and so forth.

I think the main concern here is that while the presence of these pesticides in the playgrounds of nearby schools are relatively small, we don’t really know how many years of playing in those schoolyards will affect the health and well-being of the children.  Long-term monitoring and study is certainly needed, and perhaps a reduction or elimination in the use of

Photo by Dorothea Lange [Public domain], via Wikimedia Commons

Photo by Dorothea Lange [Public domain], via Wikimedia Commons

pesticides is the safer choice for both humans and the environment.

It is also somewhat concerning that there were several pesticides identified in this study that were reportedly not used by either vineyard.  This means that either the vineyards are hiding something, or more likely, pesticide residues from farms or vineyards even further away are ending up in the air, dust, and grass of the schools.  Where are these extra pesticides coming from?  How far did they travel to get there?  How close is too close for agricultural fields that utilize pesticides?

While the results of this study were interesting, they only bring up more questions (which is good!  That’s how you “do” science….).  Due to the very limited budget, staff, and time, the authors were not able to address many of these other questions.  I think the results of this pilot-style study do raise some red flags in terms of the effects of pesticides on human and environmental health, and more long-term studies should be performed.

What do you all think of this study?  Did you have any questions that I didn’t mention?  Please feel free to leave any comments you might have about this topic!

Source: Dalvie, M.A., Sosan, M.B., Africa, A., Cairncross, E., and London, L. 2014. Environmental monitoring of pesticide residues from farms at neighbouring primary and pre-school in the Western Cape in South Africa. Science of the Total Environment 466-467: 1078-1084