Discussion |
The purpose of this study was to test the hypothesis that bioplastic degrades at a faster rate than oxo-biodegradable plastic. Through experimentation, the hypothesis was disproven. Statistically significant findings were that the decomposition rate of bioplastic is higher than the rate of decomposition of oxo-biodegradable plastic, and that the rate of decomposition of oxo-biodegradable plastic is very similar to that of synthetic plastic. Standard deviation was very low, and a student’s t-test concluded that the p-value (chance of a Type II error) was less than 0.001% in two out of three comparisons. This study had a large sample size of 30 samples per control group. Large sample size is important because it controls for the risk of reporting a false-negative finding by reducing probability of samples being irregular[3].
It is counter-intuitive that oxo-biodegradable plastic underwent virtually no biodegradation throughout the course of the experiment. This is because oxo-biodegradable plastic is endowed with a pro-degradant, which is a catalyst specialized to promote decomposition. From these results, we can only deduce that either the pro-degradant is ineffective in promoting biodegradation, or that the function of this mechanism was inhibited somehow throughout the process of the experiment. It seems more probable that the former was the reality because both precipitants for its activation were present throughout the experiment (sunlight and oxygen).
Oxo-biodegradable plastic was developed to reduce the mass of plastic in landfills[4], but with the consideration of these findings, we can know that bioplastic will be more likely than oxo-biodegradable plastic to achieve this goal. It will also, in the long term, be more likely to solve the litter crisis by reducing plastic build up in the environment. Therefore, it would be wise to concentrate industrial efforts into producing more bioplastic bags rather than into producing more oxo-biodegradable bags. Although, we must exercise caution in making such a generalization because it may very well be the case that the superlative decomposition speed of bioplastic samples observed in this study is a trait unique to the specific type of bioplastic that was used: starch-based bioplastic manufactured by Biobag. Because there is uncertainty in this regard, more research must be done on the decomposition rates of specific subcategories of bioplastic, before any convictions can be made in regards to where compostable plastic manufacturing efforts should be focussed. As well, we cannot be certain that the low levels of decomposition achieved by oxo-biodegradable plastic samples in this study are apparent in all oxo-biodegradable products on the market. Similarly, we must first perform experiments studying the decomposition abilities of other oxo-biodegradable products to achieve certainty on this matter.
While the exceedingly low standard deviation amongst all experimental groups and the exceptionally low p-value that was derived from the student's T-test that was performed both inspire much confidence in the results of the study, there are some possible sources of error that must be accounted for. The snow and ice that was present at the site of the experiment for the majority of the experiment is likely to have interfered with the decomposition process by killing microorganisms and inhibiting them from metabolizing the plastic. Thus, the results of this study may not be representative of the true decomposition rates of each type of plastic that was investigated. However, the conclusion drawn from the comparison of the results may still be valid if no other factors affected the individual samples, because all samples were subjected to the same sub zero temperatures and encased in ice and snow to the same degree.
Variables that may have affected the validity of the comparison of decomposition abilities amongst the experimental groups are as follows. After the experiment, some of the bags were washed in warm water, while others were washed in cold water. Although the process undertaken to dry the plastic samples was exhaustive, there is still a possibility that this may have affected the recorded masses of some samples. Cold water is slower to evaporate than hot water, so samples washed in cold water are more likely to have retained water during the drying process, and are therefore also more likely to have inaccurately massive recorded masses.
It is also possible that some portions of the lawn retained higher concentrations of micro-organisms than others, and that as a result, some samples received more exposure to micro-organisms. Were this the case, it is probable that some bags underwent more decomposition than others as exposure to higher numbers of micro-organisms leads to greater opportunity for microbial feeding. Finally, samples may have sustained varying levels of fine dirt and debris on their respective surfaces when measured for mass for a second time despite the extensive cleaning process that they were subjected to, and this may have affected the accuracy of mass measurements. Evidence supporting this possibility is that the control group, synthetic plastic, underwent an increase in mass over the course of the experiment according to the results, and this can only be explained
It is counter-intuitive that oxo-biodegradable plastic underwent virtually no biodegradation throughout the course of the experiment. This is because oxo-biodegradable plastic is endowed with a pro-degradant, which is a catalyst specialized to promote decomposition. From these results, we can only deduce that either the pro-degradant is ineffective in promoting biodegradation, or that the function of this mechanism was inhibited somehow throughout the process of the experiment. It seems more probable that the former was the reality because both precipitants for its activation were present throughout the experiment (sunlight and oxygen).
Oxo-biodegradable plastic was developed to reduce the mass of plastic in landfills[4], but with the consideration of these findings, we can know that bioplastic will be more likely than oxo-biodegradable plastic to achieve this goal. It will also, in the long term, be more likely to solve the litter crisis by reducing plastic build up in the environment. Therefore, it would be wise to concentrate industrial efforts into producing more bioplastic bags rather than into producing more oxo-biodegradable bags. Although, we must exercise caution in making such a generalization because it may very well be the case that the superlative decomposition speed of bioplastic samples observed in this study is a trait unique to the specific type of bioplastic that was used: starch-based bioplastic manufactured by Biobag. Because there is uncertainty in this regard, more research must be done on the decomposition rates of specific subcategories of bioplastic, before any convictions can be made in regards to where compostable plastic manufacturing efforts should be focussed. As well, we cannot be certain that the low levels of decomposition achieved by oxo-biodegradable plastic samples in this study are apparent in all oxo-biodegradable products on the market. Similarly, we must first perform experiments studying the decomposition abilities of other oxo-biodegradable products to achieve certainty on this matter.
While the exceedingly low standard deviation amongst all experimental groups and the exceptionally low p-value that was derived from the student's T-test that was performed both inspire much confidence in the results of the study, there are some possible sources of error that must be accounted for. The snow and ice that was present at the site of the experiment for the majority of the experiment is likely to have interfered with the decomposition process by killing microorganisms and inhibiting them from metabolizing the plastic. Thus, the results of this study may not be representative of the true decomposition rates of each type of plastic that was investigated. However, the conclusion drawn from the comparison of the results may still be valid if no other factors affected the individual samples, because all samples were subjected to the same sub zero temperatures and encased in ice and snow to the same degree.
Variables that may have affected the validity of the comparison of decomposition abilities amongst the experimental groups are as follows. After the experiment, some of the bags were washed in warm water, while others were washed in cold water. Although the process undertaken to dry the plastic samples was exhaustive, there is still a possibility that this may have affected the recorded masses of some samples. Cold water is slower to evaporate than hot water, so samples washed in cold water are more likely to have retained water during the drying process, and are therefore also more likely to have inaccurately massive recorded masses.
It is also possible that some portions of the lawn retained higher concentrations of micro-organisms than others, and that as a result, some samples received more exposure to micro-organisms. Were this the case, it is probable that some bags underwent more decomposition than others as exposure to higher numbers of micro-organisms leads to greater opportunity for microbial feeding. Finally, samples may have sustained varying levels of fine dirt and debris on their respective surfaces when measured for mass for a second time despite the extensive cleaning process that they were subjected to, and this may have affected the accuracy of mass measurements. Evidence supporting this possibility is that the control group, synthetic plastic, underwent an increase in mass over the course of the experiment according to the results, and this can only be explained