Persistant Organic Pollutants (POP's) in the Environment
AC 002 (10/99)
Persistent Organic Pollutants (POPs) in the Environment
Mary Jane Incorvia Mattina
Department of Analytical Chemistry
The Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, Connecticut 06504-1106
Telephone: (203) 974-8449 Fax: (203) 974-8502
BackgroundPersistent Organic Pollutants, frequently referred to by the acronym POPs, are a group of chemicals, most of which are synthetic, some of which are naturally occurring. Most POPs of international concern are synthetic organochlorine compounds, that is they contain carbon and chlorine. Some of these chemicals are pesticides such as DDT, aldrin, mirex, toxaphene, heptachlor, and chlordane; some have primarily industrial application such as the polychlorinated biphenyls (PCBs); and some are the unintentional byproducts of industrial operations, such as dioxins and furans.
All POPs have several common characteristics. As the name implies, once introduced into the environment, either intentionally by industry, as an agrochemical, or unintentionally as a byproduct, they remain in the environment for years, sometimes decades. This stability is due to their very slow chemical and biological degradation. However, these chemicals transfer into the vapor phase and so can be atmospherically transported to sites far distant from the site of initial introduction. More detailed information is available in references (1, 2).
Another common property of POPs is their very low solubility in water along with high solubility in non-aqueous media such as fats and oils. This latter property leads to their high bioaccumulation in fatty tissue. The implication of POPs in human endocrine disruption and nervous system disorders is exacerbated by their bioaccumulation factors.
ChlordaneMany of the chlorinated synthetic pesticides which are now designated as POPs were introduced commercially in the 1940s and 1950s. Among these agrochemicals is technical chlordane, a mixture of over 140 components. Technical chlordane, sold both as a dust and a liquid formulation, was used as an insecticide in commercial agricultural operations to control pests such as the tobacco budworm and Japanese beetle. For residential applications it was used for grub control in lawns and was also labeled as an herbicide. It is perhaps best known as a termiticide. Many residential foundations were treated at high rates with technical chlordane. In fact its longevity in soil made it the termiticide of choice, the very property which today renders it a public health issue.
All uses of technical chlordane and chlordane containing products were prohibited in the United States beginning in 1988. However, domestic manufacture for export continued until 1997 when its production in the U.S. was voluntarily discontinued. Although many industrial countries have banned its use, it remains in use in India and China.
Chlordane Residues in SoilBecause of its extensive use in both commercial and residential applications, its application at very high rates, as well as analytical considerations, we have chosen to investigate chlordane as a representative POP. In 1997 and 1998 our laboratory conducted a survey of chlordane residues in Connecticut soil as a function of land use. Table 1 summarizes some of our data.
Table 1. Chlordane Residues in Connecticut Soil.
|Land Use||N||Range in ppm||Average + / - stdev|
|Residential Lawn/Garden||33||5.13 to 0.001 (nd)||0.26 + / - 0.92|
|Residential Foundation||43||57.94 to 0.010 (nd)||7.48 +/- 14.56|
|Agricultural||51||0.529 to 0.008||0.148 + / - 0.118|
In the above table N is the number of soil samples of a particular land use type which were analyzed and "nd" indicates that for some samples no chlordane was detected. The survey data in the table show that chlordane residues in foundation soils averaged the highest. This is reasonable in light of the application rate of technical chlordane as a termiticide. Further research conducted in our laboratory showed that the vertical and horizontal mobility of chlordane in soil is minimal and that the degradation rate in typical Connecticut soil is very slow. The technical description of the mobility and degradation studies is presented in reference (3).
Chlordane Uptake by Food CropsData from the annual pesticide residue survey of produce sold in Connecticut suggested that some food crops preferentially contain chlordane (4). These observations prompted us to investigate the uptake of chlordane by twelve food crops in both greenhouse and field trials. While each of the twelve crops appeared to uptake chlordane from the soil, not all crops translocated chlordane to edible plant tissue. Some of the information from these studies is summarized in Table 2.
Based on the absence of chlordane in edible tissue, we rank the following crops as non-uptakers: tomatoes, peppers, corn. Due to the presence of chlordane in edible tissue we ranked the following crops uptakers: spinach, lettuce, beets, carrots, zucchini, dandelion, potatoes. The following crops contained trace amounts of chlordane in their edible tissue: eggplant, beans.
Table 2. Uptake of Chlordane by Food Crops.
|Crop, Variety||Scientific Name||Edible Tissue|
|carrot "Scarlet Nantes"||Daucus carota||Yes|
|lettuce "Salad Bowl"||Lactuca sativa||Yes|
|beets "Early Wonder Smooth Leaf"||Beta vulgaris||Yes*|
spinach "Vienna Hybrid"
|zucchini "Black Beauty"||Cucurbita pepo||Yes|
|bush beans "Provider"||Phaseolus vulgaris||Trace|
|eggplant "Neon"||Solanum melongena||Trace|
|tomato "Better Boy Hybrid"||Lycopersicon esculentum||
|potato "Red Norland" & "Superior"||Solanum tuberosum||Yes|
pepper "Blockbuster Hybrid"
|corn "Bicolor"||Zea mays||No|
*Contains chlordane in both root and leaf tissue.
SuggestionsData from our marketbasket survey indicate that POPs residues in produce sold in Connecticut are well below the action level of 0.1 ppm established by U.S. EPA for these compounds (4). However, we suggest that consumers take the following steps to reduce their dietary intake of chlordane based on our studies to date.
- All crops should be thoroughly washed so that all traces of soil are removed.
In addition to scrubbing root crops to remove all traces of soil, peeling of root crops is also prudent.
- For the home garden if no information is available regarding termiticide treatment around the foundation or if termiticide is known to have been applied, it is prudent not to plant within one foot of the foundation. This is particularly important for spinach, lettuce, beets, carrots, zucchini, dandelion, potatoes.
3. M.J.I. Mattina, W. Iannucci-Berger, L. Dykas, J. Pardus. Environ Sci. Technol 1999. 33:2425-2431
4. H.M. Pylypiw, T. Misenti, M.J.I. Mattina. Bulletin 940. The Connecticut Agricultural Experiment Station.