High Sierra Topix

Pesticides, DDT Found In Animals At Sequoia National Park

CBS SF Bay Area
April 25, 2016 2:36 PM
http://sanfrancisco.cbslocal.com/2016/0 ... onal-park/



SAN FRANCISCO (KCBS) – A new study on the long term impact of agricultural pesticides has found traces of so-called “legacy pollutants” including DDT in Western pond turtles, insects and soil sediment at Sequoia National Park.

Brian Todd, an associate professor of wildlife, fish and conservation biology at UC Davis co-authored the study. Todd said controlling the flow of pesticides into national parks is pretty much impossible.

“Sequoia National Park is very interesting, because it begins in the foothills, just downwind of very heavy agricultural land in the southern part of the Central Valley,” Todd told KCBS. “It tends to accumulate from drift and runoff, a lot of the pesticides that have been used over the last several decades.”

Todd says the study focused heavily on turtles because they are what’s known as an “indicator species,” whose reaction to changes in the environment serves as a kind of barometer of those changes.

Previous studies have shown pesticide exposure leads to neurological damage in the turtles.

The findings were published in the online journal Chemosphere.

INTRODUCTION

DDT is an organochlorine insecticide used mainly to control mosquito-borne malaria; use on crops has generally been replaced by less persistent insecticides (1). It was extensively used during the Second World War among Allied troops and certain civilian populations to control insect typhus and malaria vectors, and was then extensively used as an agricultural insecticide after 1945 (3). DDT was banned for use in Sweden in 1970 and in the United States in 1972 (3).

ENVIRONMENTAL FATE

Breakdown in Soil and Groundwater

DDT is very highly persistent in the environment, with a reported half life of between 2-15 years (15, 16) and is immobile in most soils. Routes of loss and degradation include runoff, volatilization, photolysis and biodegradation (aerobic and anaerobic) (3). These processes generally occur only very slowly. Breakdown products in the soil environment are DDE and DDD, which are also highly persistent and have similar chemical and physical properties (12, 16).
Due to its extremely low solubility in water, DDT will be retained to a greater degree by soils and soil fractions with higher proportions of soil organic matter (12). It may accumulate in the top soil layer in situations where heavy applications are (or were) made annually; e.g., for apples (2). Generally DDT is tightly sorbed by soil organic matter, but it (along with its metabolites) has been detected in many locations in soil and groundwater where it may be available to organisms (12, 15). This is probably due to its high persistence; although it is immobile or only very slightly mobile, over very long periods of time it may be able to eventually leach into groundwater, especially in soils with little soil organic matter.

Residues at the surface of the soil are much more likely to be broken down or otherwise dissipated than those below several inches (14). Studies in Arizona have shown that volatilization losses may be significant and rapid in soils with very low organic matter content (desert soils) and high irradiance of sunlight, with volatilization losses reported as high as 50% in 5 months (17). In other soils (Hood River and Medford) this rate may be as low as 17- 18% over 5 years (17). Volatilization loss will vary with the amount of DDT applied, proportion of soil organic matter, proximity to soil-air interface and the amount of sunlight (12).