Further research for this experiment would be to figure out a way to test for chemicals used in pesticides directly. If a method was developed to test for pesticides, one could test to see if a TDS meter is accurate in detecting for pesticides or harmful chemicals. Another branch off of this experiment would be to see if other produce is as contaminated as apples, or if say strawberries are more contaminated than blueberries. The produce world is huge and there are many different ways to explore commercial produce and noncommercial produce.
For other researchers attempting an experiment similar to this, be very mindful of where you are getting your produce. At first we had purchased Yates apples assuming that they would serve as a portion of the noncommercial data, but upon further investigation, it was found that they outsource many of their products. When we discovered this, the Yates apples were forced into the commercial category. So, a word to the wise, be wary of what a retailer claims and what they actually sell.
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After the trials were conducted, the results were analyzed with a descriptive analysis, and a 2-sample T-Test. The figure above shows the TDS of the commercially produced apples and non-commercially produced apples in a box plot. The plot shows that all the TDS data for non commercial apples fell between 1 ppm and 4 ppm, presenting that the data had a range of 3 ppm . The median for the TDS of non-commercially produced apples is 2 ppm, and the median of the TDS of the commercially produced apples is 3 ppm. The data for the commercially produced apples is skewed to the left meaning that more data points are to the left of the range of data points. The majority of the data points or the interquartile range of non-commercially produced apples 1 ppm, commercially produced apples 5 ppm range, showing little spread or variability. Both interquartile ranges overlapped showing similarity in TDS, and majority of the commercially produced apples were from Yates and they produced similar results to non commercially produced apples. The outliers of the commercially produced apples were kept since they prove to be significant in the data since the outliers were mainly from apples that were coated in wax. If the outliers were removed, it would leave a major component of the commercial apple population out. Thus the outliers were kept.
After running the T-Test, the researchers reject the null hypothesis because the p-value of 0.0003 is less than the α level of 0.05. P-value is the probability of getting the results, given that the null hypothesis is true. There is evidence that commercially produced apples and non-commercially produced apples have a difference in TDS. The apples that were outliers were the ones that was coated in wax and were deemed significant to the research so it could not have be omitted. The commercially produced apples’ elevated level of contamination can be attributed to the greater amount of total dissolved solids in the water after washing. These dissolved solids can range from dust and dirt to potentially potent chemicals. If it were to be chemicals, the cations and anions in the pesticides used to mass produce the crop could be a potential source for such a high reading. Pesticides commonly contain arsenic, mercury(I), chromium(III) and lead(II) which have charges of 3-, 2+, 3+, and 2+ respectively (U.S. National Library of Medicine). These large charges block a pest or insects’ neurotransmitters from delivering information to other parts of its body, thus disrupting its body’s natural processes. The insect’s body cannot receive the information it needs to function via electrical pulses, it’s muscles become over stimulated leading to paralysis and ultimately death (Ganzel). Since pesticides are designed to block electrical pulses in an insect, they will also block electrical pulses in other life forms or water. Total dissolved solids in water is defined as salts, minerals, metals, anions and cations in water as measured by electrical currents sent through the water (Oram). Thus pesticides that inhibit electrical currents through high charged cations and anions would then greatly increase the TDS reading in any water sample being tested. The average TDS reading for the commercially produced apples was proved to be significantly higher than that of the non commercially produced apples. Although not all of the commercial apples had high TDS levels indicating large amounts of residual chemicals, the 15 that did could be due to inconsistencies in how pesticides are sprayed onto the apple trees. Apples that were directly sprayed with pesticides are more likely to retain higher traces of pesticide residue even after going through preparations for commercial sale. The noncommercial apples that were tested in this experiment were grown without the aid of pesticides. Major difference in the TDS readings of the apple groups is thought to be pesticides, however there is another potential culprit. Commercial apples are often coated with a thin layer of wax, which is known to be a resistor of electrical current. Wax is a nonpolar organic compound, meaning that it has no free electrons to carry an electrical charge (Smith). Thus it blocks electrical currents similar to the cations and anions discussed in the pesticides. So Wax could be another component in the raised level of TDS in the commercially produced apples. An easier method of testing for residual material (potentially pesticides) was developed with this research. Most previous research had used high tech laboratory equipment to analyze test samples, or used methods out of reach from the normal population. The testing methods in this research are more feasible for the average person, since the materials are easy to gather. The impact on the scientific community is that a potentially new and more accessible method of testing the cleanliness of produce which ultimately allows consumers to ensure that their food is safe. This research as any experiment contains errors. All apples have different attributes, one being size, which directly relates to surface area. With a larger surface area there is a larger possibility of an increase in TDS. Also some apples may have had holes in the peel, the flesh inside could have been exposed to the water leading to a high TDS. To improve the research base on this knowledge, the apples are to be tested should be measured and categorized by size and a closer examination of the apple should be done to inspect for any malformations. Different testing method could also be conducted to test for pesticide such as the nitrate test which is costly. The research shows that the TDS can be used as an affordable at home method to see how clean one’s produce is, but it will only show the TDS and not the exact amount of pesticide. Many do not have a second thought when eating an apple without washing. Now, consumers are taking more notice to what they are purchasing: the process which the produce has gone through and what it is composed of. The research shows that there are residual materials on apples. The official trials were conducted the same way as the pre-trials; the same processes were followed. In the end, 75 commercial trials were conducted. The commercial apples were bought from Yates and Meijer. It may seem odd that Yates is classified as commercial, but not all of their apples are from their orchards. Often times places like Yates outsource to meet their demand. A total of 91 noncommercial apples were tested. The noncommercial apples were acquired from Mr. Grobbel (a local independent produce seller), and Farmer Rick (a friend of the researcher's family). Right away some differences in the trials could be seen. The commercial apples from Meijer had a waxy coating. This not only raised the TDS contamination in the water, but it also did not look appealing. However, some trials from Yates appeared to have little to no contamination at all. Examples of the commercial trials can be seen below. The non commercial apples were relatively consistent with the amount of dirt in the beaker. They also had no drastic change in appearance. Examples of the remnants left in the beaker are shown below.
What was done? 20 pre-trials were completed with 10 commercial apple and 10 non comercial trials.
Both researchers have an interest in gardening, so when formulating a topic to explore residual pesticides on produce became a topic of interest. After investigating, we found that to determine pesticide specific residue would require expensive laboratory equipment. It was then that a total dissolves solids (TDS) meter was brought to our attention. A TDS meter would allow us to calculate residual material left on an item after being rinsed with water, by taking a before and after reading. Thus our topic for research is determining whether roadside or grocery store apples have the least amount of residual material on them.
This far, we have drafted emails to send out to three university professors of agriculture in order to have some insight into what they recommend, their opinions and overall thoughts on the topic. In addition to a prospective professional contact, 12 sources have been collected and reviewed in regards to the research being conducted. The majority of them were found through google scholar, with some being found through universities and MeL. The sources that were found in pesticide and residual material testing only used professional laboratory equipment that is out of our hands. Some methods that were conducted rinsed produce then tested the water, but again did not use a TDS meter. Our research will be one of the first to use the TDS meter method for finding residual materials on produce. |
ReshearchersSenior at Macomb Math Science and Technology Center Archives
December 2017
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