Pesticide exposure is a prevalent problem prevalent in California and worldwide. Soil pesticides can drift into homes and people can become sick. These pesticides have been sprayed on a crops a century. The Environmental Protection Agency has reviewed hundreds of pesticides. Many have been banned because they have been found to endanger human health an
Chlordane has been banned because the EPA has found it harmful to the central nervous system and causes organ damage in mammals, birds, and fish. Although all approved chlordane uses were discontinued by the US in 1988, the chemical can still be detected in creeks and streams because of the persistence of its high sediment binding strength. Chlordane is not water-soluble (Log Kow = 2.78), but it does leech into water, bioconcentrate, and bioaccumulate. The pesticide tightly binds to organic soil because it has low polarity therefore the highest chlordane concentrations are found in creek sediments.
Sediment from several locations along Tecolote Creek in San Diego, CA were analyzed for persisting chlordane levels: Tecolote Creek (TC), Fiesta Cudahy Creek (FC), a reservoir (RS), a transformer (TR), the Cadman park lawn (CA), the YMCA (YM), and a baseball field lawn (BB).
This figure below reports the GPS locations of the analyzed sites.
A chlordane residue extraction was performed on each sample and an enzyme-linked immunosorbent assay (ELISA) analysis determined its chlordane concentration. ELISAs combine the specificity of antibodies with the sensitivity of simple enzyme assays, by using antibodies or antigens coupled to an easily-assayed enzyme to provide useful measurements of antigen or antibody concentration.
The lowest concentrations were found in the YMCA (YM) and Cadman Park (CA) sediments. Fiesta Creek (FC) and the Reservoir (RS) sediments showed very high levels of the pesticide contamination. The Telecote Creek location shows a decrease from 560 ppb to less than 200 ppb.
Each sample was also tested for CaCO3 contents, organic material contents, acidity levels and distribution of particle size. Each sample was pre-weighed; vacuum filtrated in hydrochloric acid (HCl) then dried. The dried samples were reweighed then the value was subtracted from the previous measurement to determine the sample’s CaCO3 mass content.
This picture shows a USD environmental chemistry student weighing sediment sample for analysis in the laboratory with proper safety wear.
Each dried sample was placed in a pre-weighed crucible and covered with a lid. A Bunsen burner heated the crucible through a clay triangle until the sample glowed. The heated sample was cooled and reweighed to determine the mass of organic content. The picture below shows the heated crucible during the organics analysis.
The video at the end of this blog posting gives a laboratory view of the procedure used to determine the sediment organic material content.
pH paper was used to determine the relative acidity of each soil/sediment sample.
The data for the three experiments is presented in the figure below:
The highest percentages of calcium carbonate were found in the Baseball Field (BB) and Telecote Creek (TC). The lowest percentages of calcium carbonate were found in the Transformer (TR) and the YMCA (YM). A correlation is expected between samples with high levels of CaCO3 and low pH. As the calcium carbonate increased the sample showed higher
acidity levels due to more weak carbonic acid content. This trend is shown in the Baseball Field (BB), Cadman (CA), and the Transformer (TR). These samples show direct relationships to acidity and carbonate content.
Particle Size Distribution was determined with molecular sieve filtering and Coulter laser particle scattering spectrometry.
The figure below shows the distribution of particles in the samples.
E Chem Blog: The Movie
http://www.youtube.com/watch?v=P7Pjp9ZHkp0
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