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Measurement of Residual Herbicide Activity in Soil

1. Introduction

Herbicide persistence is the length of time an herbicide remains active in the environment after application (Curran, 2016). Chemical properties, environmental conditions, etc. can affect persistence. Factors such as the chemical nature of the herbicide such as solubility, volatility, and binding affinity to soil particles can affect the duration of the herbicide in soil or water. Environmental conditions such as temperature, humidity, and sunlight exposure can also affect herbicide degradation rates (Bailey, 2003). Bioassay is a scientific method used to measure the biological effect or potency of a substance by exposing an organism or biological system to different concentrations or doses of the substance and observing the resulting response (Langfield et al., 2004). Bioassays have an important role in herbicide research. For effectiveness, researchers can assess the ability of an herbicide to inhibit weed growth or cause weed death. For mode of action, by studying the response of target plants or plant tissues to herbicides, researchers can gain insight into the physiological and biochemical processes affected by herbicides. For potential impacts, by exposing non-target plants or organisms to herbicides, researchers can assess their sensitivity and potential impacts on ecosystems (Hollaway et al., 2002). In this experiment, different concentrations of 2,4-D were added to different soil conditions to observe its effect on the root growth of cucumber seeds.2,4-D acts in a hormone-disrupting manner, acting as a synthetic auxin that leads to uncontrolled growth and developmental abnormalities in susceptible plants, resulting in effective control of pre- or postemergence weeds (Kearns et al., 2014).

2. Methods

In this Section, please refer to Department of Biology, 2023, Biology 354 Environmental Toxicology 1 Manual, Experiment 3: Measurement of Residual Herbicide Activity in Soil, pp. 28-34, etc.

3. Results

3.1 Sample Calculation.

For the calculation of the average of the data, add up all the data and divide by the amount of data. For example, if the average root length of a group is 18.6mm, 17.4mm, and 14.8mm, their average is (18.6+17.4+14.8)/3=16.9mm.

For the calculation of standard deviation, find the mean of the data set, calculate the squared difference between each data point and the mean, find the mean of the squared differences, and take the square root of the variance to get the standard deviation. For example, if a set of root lengths is 18.6, 17.4, and 14.8, then the mean is 16.9, the squared deviation is 2.89, 0.25, and 4.41, and the mean of the squared deviations is 7.55, which gives a standard deviation of 2.75.

For the calculation of the corrected concentration of 2,4-D, [2,4-D] = solution added × [concentration of standard]/final wet weight. For example, with a standard of 0.0001 µg/mL, 100 g of sand is added to the plate, and 11 mL of water is added, the µg 2,4- d / g wet sand is: [2,4-D] = 11 mL × 0.0001 µg/mL (100g + 11g) = 9.91 × 10-6 µg/g.

3.2 Standard curve data for sand from Test 1

Table 1. Mean and standard deviation data for the sand from Test 1.

Figure 1. Standard curve for the 2,4-D in sand from Test 1.

Table 1 shows the mean root length and standard deviation of each group in Test1 at different 2,4-D concentrations in the sand, as well as the mean 2,4-D concentration for the whole group and the mean standard deviation for the whole rent, along with the corrected 2,4-D concentration.

Figure 1 shows the relationship between 2,4-D and mean root length in different concentrations of sand, along with the standard deviation of mean root length.

3.3 Sand batch treatments from Test 2

Table 2. Sand batch treatments data from Test 2.

Table 2 shows the mean root length as well as standard deviation of each set of cucumber seeds in different sand Batch.

3.3 Standard curve data for promix from Test 3

Table 3. Mean and standard deviation data for the promix from Test 3.

Figure 2. Standard curve for the 2,4-D in promix from Test 3.

Table 3 shows the mean root length and standard deviation of each group in Test3 at different concentrations of 2,4-D in promix, as well as the mean 2,4-D concentration for the whole group and the mean standard deviation for the whole rent, along with the corrected 2,4-D concentration.

Figure 2 shows the relationship between 2,4-D and mean root length in different concentrations of promix, while the standard deviation of mean root length is also shown in the figure.

3.4 Promix batch treatments from Test 4

Table 4. Promix batch treatments data from Test 4.

Table 4 shows the average root length of each set of cucumber seeds in different promix Batch along with the standard deviation.

4. Discussion

The slope of the folded plot fitted curve in Figure 1 is -6.405 and the slope of the folded plot fitted curve in Figure 2 is -5.026, both of which are negatively correlated. The results indicate that herbicide residues in either Promix or sand can have a growth inhibiting effect on the root length of cucumber seeds. The slope of the curve in Figure 1 is smaller than the slope of the curve in Figure 2, which suggests a more rapid change and a greater effect. It can be introduced that the residual activity of 2,4-D in sand is stronger than that in Promix.

For the study of 2,4-D residual activity in sand, by using the data in Table 2, for the first group (Batch 1 and 2), the average root length of Batch 1 was 15.88 mm, and the average root length of Batch 2 was 16.17 mm. for the same incubation time, the group with higher temperature had longer root lengths, which suggests that the higher the temperature, the lower the residual activity of 2,4-D in sand. . Higher temperatures usually accelerate the degradation of 2,4- d in soil. Under warmer conditions, microbial activities, chemical reactions and photodegradation processes tend to occur at a faster rate (Crespín et al., 2001). Batch 1 and Batch 3 were experimental groups with different incubation times under the same temperature conditions. The average root length was 15.88 mm for Batch 1 and 14.34 mm for Batch 3. The data showed that the longer the incubation time, the shorter the average root length was, which suggests that with incubation time increases, the residual activity of 2,4-D decreases (Voos & Groffman, 1997). Regarding the effect of organic matter on 2,4-D residual activity, organic matter in the soil, such as humus and decomposed plant matter, has a strong affinity for 2,4- d herbicides. This means that organic matter can adsorb or bind herbicide molecules, reducing their effectiveness for plant uptake. As a result, 2,4- d may be less effective in controlling target weeds (Kearns et al., 2014). In addition, the amount and type of organic matter in the sand can affect the residual activity of 2,4- d. The amount and type of organic matter in the sand can affect the residual activity of 2,4-d (Cox et al., 2000). Soils with higher organic matter content have a greater ability to bind 2,4-d than soils with lower organic matter content, which reduces its effectiveness in controlling weeds and shortens its residual activity (Benoit et al., 1996).

For the study of 2,4-D residual activity in Promix, by the data in Table 4, the group with higher temperatures had longer root lengths for the same incubation time, and soilless media like Promix may have slower degradation of 2,4- d in Promix compared to natural soil due to limited microbial activity. This may prolong the residual activity of the herbicide. And higher temperatures usually accelerate the degradation of 2,4- d, which means that the residual activity of the herbicide in Promix may be shorter (Aulakh & Jhala, 2015). Regarding the incubation time, the data in Table 4 show that at the same temperature, the longer the time, the longer the root length. This suggests a decrease in 2,4-D activity and a weakening of inhibition. For organic matter, Promix has a low organic matter content. In soils with limited organic matter content, adsorption of 2,4- d to Promix is usually low. This could increase the effectiveness of 2,4- d for weed control and may prolong its residual activity (Craigmyle et al., 2013).

Question

1. I may use chemical exclusion and sample analysis (Leitner et al., 2012). For the former, a full-scale screening using special chemical reagents ultimately narrows down the characteristics of the herbicide (Tan et al., 2022). For the latter, samples are taken locally and sent to a university laboratory or a specialized research facility for methods such as spectrophotometric analysis to determine the extent of the herbicide from the characteristics of the substance.

I do not believe that complex physicochemical methods are necessary because it may not always be necessary to identify specific herbicide residues. We can use centrifuges, chromatography, etc. to target a particular characteristic of the herbicide to identify it.

2. Atrazine is present in several areas including surface water, groundwater, and soil. Atrazine has been detected in rivers, lakes, and drinking water sources in areas of intensive corn cultivation (Solomon et al., 1996).

Atrazine has been linked to a variety of adverse health effects, including reproductive and developmental problems, hormonal disturbances, and a potential link to certain cancers (De Albuquerque et al., 2020).

Potential effects on people include hormonal disruption; atrazine has been shown to interfere with the production and release of hormones such as estrogen, testosterone, and thyroid hormones, which may lead to hormonal imbalances and related health effects (Gammon et al., 2005). There is also drinking water contamination, where runoff from agricultural fields can carry atrazine into surface and groundwater, resulting in elevated levels of atrazine in drinking water supplies.

Potential effects on other organisms, such as the combined stress effects of atrazine and cadmium on earthworms, which could lead to its enhanced toxicity, and the combined exposure of atrazine and cadmium could lead to enhanced toxicity to earthworms. Both compounds are toxic, and their combined action may trigger more intense toxic effects and pose a greater threat to the survival and health of earthworms (Wang et al., 2012).

Atrazine has acute effects such as irritation and toxicity, and acute exposure to atrazine can cause eye and skin irritation, respiratory distress, nausea, vomiting and gastrointestinal distress (Foradori et al., 2009).