PESTICIDES IN FRUITS AND VEGETABLES: NATURAL VS. ORGANICALLY GROWN FOOD
Before the lab experiment begins, you must bring in a naturally and organically grown fruit or vegetable of choice.
biology, agriculture, organic chemistry, food industry, toxicology
A pesticide is any substance or mixture of substances intended to prevent, destroy, or mitigate any pest. Pests can be insects, mice, other annoying animals, unwanted plants (weeds), fungi, or microorganisms, like bacteria and viruses. Under United States law, a pesticide is also any substance or mixture of substances intended for use as a plant regulator, defoliant, or desiccant. By their very nature, pesticides are designated to kill or otherwise adversely affect living organisms. Thus, they are harmful to humans, animals, or the environment. Simultaneously, pesticides are useful to society because of their ability to kill potential disease-causing organisms, as well as, control insects, weeds, or other pests. Pesticides have also helped the farming industry become more stable by increasing crop production to meet the demands of the worlds population. Pesticide, herbicide, insecticides, and fungicides have been widely used since the Post-World War II era up until the present.
DDT (dichlorodiphenyltrichloroethane) is one of the most well known pesticides. It was banned from use in the early 1970s for its effect on bird eggshells. DDT was once very useful in the production of bigger and juicer fruits. It's positive effects are preventing pests, killing bugs and making homes safer for kids, and killing horn flies and other pests, allowing cows to grow fatter. Other banned organochlorine pesticides are aldrin, dieldrin, and heptachlor. Endrin was banned in 1992. All isomers of BHC are also banned due to their potential to cause cancer. Today, some of those banned pesticides can be detected in fruits and vegetables because they are not easily biodegradable and are insoluble in water.
During the last 30 years, an increasing number of pesticides present in the atmosphere and rainfall have been reported and well documented. It is the result of drift during applications, volatilization from treated surfaces, and wind erosion of soil. Recent research conducted by Heberer and Dunnbier ( Environ. Sc. Technol. 1999; 33, 2346-2531) have proved that DDT is distributed globally by atmospheric transport. Once the pesticides enter the atmosphere, they can be transported for a certain distance away from its application site. This is especially true for organochlorine pesticides; they have been detected in remote regions such as the North and South Poles. They have also been found in arctic mammals which eat the contaminated fish. DDT residues are extremely persistent in the environment and degradation strongly depends on the environmental conditions. It was demonstrated that forms of DDT, or its metabolite, form residues in seawater, surface water, ground water, or drinking water (Kumari et al. Environ. Contam. Toxicol, 1996, 57, 787-793). Therefore, it may also be found in fruits, vegetables, or seafood, even though there is no direct use of those banned pesticides on our food.
Pesticides may harm a developing child by blocking the absorption of important food nutrients necessary for normal healthy growth (Raloff and Pendick, Science News 1993, 1444, 4-5). Another time pesticides may cause harm to humans is during the development of the child's excretory system. Under such conditions, the body may not be able to fully remove pesticides. There are "critical periods" in human development when exposure to a toxin can permanently alter the way an individual's biological system operates. It is important that pesticides are easy to remove by washing and have short half-lives, so that its harmful effects will not affect humans who eat fruits and vegetables..
"Organically grown" food is processed using no synthetic fertilizers or pesticides. Pesticides derived from natural sources (e.g. biological pesticides) may be used in producing organically grown food. Increasingly, some consumers are purchasing organically grown food as a way to reduce their exposure to synthetic pesticides or fertilizers. Organic products sell for a higher price, and they are usually smaller in presence. They may also contain some bugs. Consumers may question whether it is worth it to buy less "attractive" organic products at higher prices. Elimination of pesticides, of course, would benefit our health, but economically, it will cause many negative effects. For example, low production yield, but higher selling price would disturb the global economy. Moreover, as it was mentioned above, there are many pesticides which cannot be avoided due to the atmospheric transport. A study by Zalom and Strand (Calif.Agric. 1990, 44, 16) showed that there are no substitutes for 30 % of the pesticides.
GLASSWARE AND ACCESSORIES:
- Kitchen blender (homogenizer), centrifuge tubes, 10 mL tubes, evaporating vessel, ENVI-carb SPE tube 57094 (6 mL tubes, 500 mg packing), rotary evaporator, 15 mL tubes, 5 mL bottles with septa caps, Hamilton syringe (10 ml),
SPBTM-608 capillary column (30 m x 0.53 mm ID, 0.50 mm film; Oven: 100 oC to 290 oC at 10 deg/min; keep at 290 oC from 30 min; carrier gas: helium, 10 ml/min, detector: ECD - 300 oC, injector: 1 mL, 250 oC.
PRINCIPLE OF THE METHOD
In this experiment 1 mL volumes of each sample extract are injected in the GC (set at the above mentioned conditions). The retention time is related to the boiling point of the species and their interactions with the stationary phase of the chromatographic column. For greater accuracy the precision, multiple injection of each sample is recommended. Peak heights, peak areas, and corresponding elution times for each sample are recorded and used in determination of pesticides Comparing their elution times to those of the standards identifies the species present in the sample.
The following steps are used in the determination procedure:
I. Determination of the calibration curve
II. Extraction of pesticides
III. Determination of the content of pesticides in samples
CALIBRATION DATA SHEET (for one concentration):
SAMPLE ANALYSIS DATA SHEET:
Prepare a laboratory report containing: