AIR QUALITY IN THE CHESAPEAKE BAY REGION AS INFLUENCED BY AGRICULTURAL LAND USE CHANGES
Title: Environmental factors affecting the levels of legacy pesticides in the airshed of Delaware and Chesapeake Bays
Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2010
Publication Date: May 14, 2010
Citation: Goel, A., Mcconnell, L.L., Torrents, A., Kuang, Z., Hapeman, C.J., Meritt, D.W., Alexander, S.T., Scudlark, J.R., Scarborough, R. 2010. Environmental factors affecting the levels of legacy pesticides in the airshed of Delaware and Chesapeake Bays. Environmental Toxicology and Chemistry. 29:1893-1906.
Interpretive Summary: Restoration of the Chesapeake Bay, a national treasure and the largest estuary in the United States, is a national priority. Federal agencies have also recently been tasked with an Executive Order to “use their expertise and resources to contribute significantly to improving the health of the Chesapeake Bay.” Residues of organic pollutants can cause toxic effects on wildlife many years after they are released. A number of chlorinated insecticides were banned in the 1960’s through 1980’s due to significant toxicity to aquatic organisms, birds, and humans. Chlordanes were used for termite control in buildings, p,p’-DDT was used for mosquito control, dieldrin, aldrin, and heptachlor were used in agricultural applications for insect control, and hexachlorocylohexanes (HCH) were used as an insecticide. One HCH called gamma-HCH or lindane is still in limited use in this country and Canada. This work represents the first long term study of these legacy pesticides in air and rain in the Chesapeake Bay region. Air and rain samples were collected over 2000-2003 from three locations on the Upper Delmarva Peninsula. Overall, the levels were found to be low and slowly declining in the region. Concentrations in rain were extremely low and were infrequently detected due to the relatively low rain sample volumes collected. An analysis of the air concentration patterns with temperature and wind speed suggest that while most of the compounds have a significant long range transport source (global background or regional background sources), agricultural soils on the Delmarva may still contain residues of diedrin, heptachlor, and DDE, the degradation product of DDT. This work suggests that concentrations of these chemicals in soils should be investigated further as potential sources to aquatic and terrestrial organisms in the Chesapeake Bay.
Weekly air (n=271) and event based rain samples (n=489) collected for the period 2000-2003 from three locations in the Delmarva Peninsula (MD and DE) were utilized to determine levels and temporal trends of legacy pesticides in the atmosphere. The goal was to assess the contribution of atmospheric input of legacy pesticides to the Chesapeake Bay where the water quality and bio-diversity of associated natural areas is on a continued decline. The samples were analyzed for 15 pesticides and degradation products using gas chromatography-mass spectrometry (GC-MS). Low frequency of detection (<10%) combined with low concentrations reveals that wet deposition is not a significant source of the target analytes to the region. However these chemicals occurred very frequently in gas phase samples (chlordane and hexachlorocyclohexanes were ubiquitous while others were present in <75% of samples) at levels that are consistent with the N-S descending transect (lower than in the Great Lakes) and appear to be decreasing at a faster rate than in the Great Lakes region (half lives < 3 yr for most chemicals). Levels of one of the most toxic legacy pesticides, p,p’-DDT, were below our method detection limits. The results suggest that levels of these chemicals will decrease more rapidly in the Chesapeake Bay region than in the Great Lakes region. The atmospheric occurrence is dependent upon the usage patterns, pesticide chemistry and environmental conditions. Temperature alone did not account for the variability in air concentrations and suggests that long range transport is not the sole source of many of these compounds to the Peninsula. An analysis of enthalpy of phase transfer indicates that dieldrin, heptachlor, and p,p’-DDE (the primary p,p’-DDT degradation product) have local sources in the region.