Spatiotemporal Differences and Ecological Risk Assessment of Heavy Metal Pollution of Roadside Plant Leaves in Baoji City, China

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

Major Points

Question 1: Plants leaves have different adsorption capacity so, how can you guess the air pollution concentration in ambient air especially in PM? 

Our response: In our study, the concentrations of heavy metals in the leaves of plants in May and November were measured.Since May is the beginning of the growth of vegetation leaves, November vegetation leaves have been mature but have not fallen, is a full cycle of leaf growth, so we choose to collect leaves in these two months. After that,the adsorption capacity of leaves of different vegetation was reflected by comparing the change of concentration.

Question 2: List all species in table 2 and need to rearrange table as some elements exhibiting mean and two elements showing CV? 

Our response: Thank you very much for your suggestions for our paper. In the revised version we have reworked Table 2 to show the complete data of our sample.

We made two modifications.

1. We added a new species, C.deodara, to the original list of species.
2. In the index row of elements in the table, change the situation that two elements in the original table show CV and other elements show average value to each heavy metal element has average value and CV index.

See lines 224 in the revised version.

Table 2. Mean element concentration, coefficient of variation (CV) of roadside plant leaves in Baoji

			Ni (mg·kg-1)		Cu (mg·kg-1)		Cd (mg·kg-1)		Pb (mg·kg-1)		Zn (mg·kg-1)
Species	Time		Mean	CV	Mean	CV	Mean	CV	Mean	CV	Mean	CV
O.japonicus (I)		May	3.07	0.45	10.57	0.30	0.40	0.88	10.60	1.15	67.49	0.35
		Nov.	3.07	0.44	13.71	0.25	0.23	0.45	4.74	1.73	52.43	0.45
L. vicaryi (II)		May	2.55	0.45	10.65	0.57	0.32	1.42	5.00	0.95	69.31	0.39
		Nov.	4.39	0.39	15.20	0.34	0.18	0.77	8.05	0.66	63.82	0.44
L. vicaryi (III)		May	1.92	0.28	8.63	0.38	0.21	0.78	3.71	0.58	56.79	0.19
		Nov.	1.79	0.47	12.73	0.29	0.12	0.57	4.67	0.55	52.49	0.42
P. acerifolia (IV)		May	3.48	0.19	13.61	0.32	0.21	0.59	9.78	0.60	65.51	0.34
		Nov.	3.79	1.05	8.56	1.06	0.09	1.56	3.41	1.56	47.69	0.77
S. japonica (IV)		May	2.52	0.21	10.41	0.31	0.11	0.34	7.17	0.45	57.69	0.23
		Nov.	11.55	0.89	14.03	0.19	0.22	0.15	11.37	0.37	73.82	0.07
C. deodara (IV)		May	3.08	0.98	7.25	0.66	0.19	0.46	30.28	1.47	85.43	0.74
		Nov.	1.73	0.12	8.38	0.51	0.13	0.77	4.19	0.03	29.65	0.55

 

Question 3: Why Ni and Cd showing higher differences between May and Nov in L. vicaryi and S. japonica? 

Our response: This was relevant with the external environment. In November, Ni and Cd in L. vicaryi were higher than those in May. This is because the collecting area of L. vicaryi is an industrial concentration area, Ni and Cd are automobile pollutants[1], L. vicaryi in November absorbed more Ni and Cd than in May. Both Ni and Cd of S. japonica were higher in November than in May, due to the construction of a new railway in July in the sampling area of S. japonica, which generated more Ni and Cd.

Question 4: PM is worsened in winter season so what is effect of seasons on heavy metal conc. and on leaves adsorption capacity? 

Our response: The accumulation of heavy metals in leaves of different vegetation types at the same height is influenced by the growth season, rainwater runoff, wind direction, external structure of leaves, internal physiological and biochemical characteristics and genetic differences. The absorption of heavy metal pollution by plant leaves will decrease obviously in winter, which is mainly due to the influence of temperature on the metabolic activity of plants, in turn, the absorption of heavy metal pollution is affected. The concentration of PM2.5 in Baoji is the highest from mid-November to mid-February, which may be due to the increase of pollutants caused by urban heating. Our research was conducted from mid-May to mid-November, so the deterioration of PM concentration had little impact on our research.

Question 5: What was wind directions and wind influence in heavy metal mixing?

Our response: In our process of samples collection,four directions of the East,the West,the South and the North were determined by GPS and collecting samples of plant leaves at the same height .The collected plant leaves were mixed to reduce the error.

Question 6: Need to describe the safe limits of heavy metals accumulation and how much it jumped in each species?

Our response: The limit of heavy metal accumulation is indicated by the P_i value. Psum ≤ 0.7 represents safe; 0.7 < Psum ≤ 1.0 represents a warning line; 1.0 < Psum ≤ 2.0 represents slight pollution; 2.0 < Psum ≤ 3.0 represents moderate pollution; and Psum > 3.0 represents heavy pollution. See lines 176-179 in the revised version. 

Question 7: What was E and RI value of campus plants?

Our response: As the background of calculating E and RI values, campus plant leaves are mainly selected in areas with relatively less artificial disturbance, no industrial pollution sources and less pollution caused by traffic. In this paper, the E value of campus plants is 5, RI value is 25.

Question 8: I recommend drawing the spatio temporal kriging map of heavy metals conc. With sampling points as figure 1(b) to clearly visualize the effect of roadside contamination and ecological risk.

Our response: Thank you for your suggestion, we added a new graph (figure 4) in the revised version, it is the spatio temporal kriging of heavy metal pollution concentration. See lines 373 in the revised version.

Minor Points

Question 1: There is shortage of technical words, need to polish.

Our response: Thank you very much for your suggestion. We have replaced some technical terms in the revised version and revised the sentences, mainly focusing on the introduction, discussion and conclusion.

Thank you very much for your suggestion. We have replaced some technical terms in the revised version and revised the sentences, mainly focusing on the introduction(lines 33-35,41-43, and 49-520, discussion (lines 295-296 and 390-391) and conclusion (lines 418-419 and 423).

Question 2: Line 14-15: How many species used in study? Write down number.

Our response: The concentration of Ni, Cu, Cd, Pb and Zn in the leaves of five different species (Ophiopogon japonicus, Ligustrum vicaryi, Platanus acerifolia, Cedrus deodara and Sophora japonica) were measured, which were from Ⅰ, Ⅱ, Ⅲ, Ⅳ (0.05 m, 0.25 m, 1 m, 4 m) at different times (May and November) in the green belt of Baoji city. See lines 14-16 in the revised version.

Question 3: Line 64-65: Restructure the sentence and clearly highlight argument.

Our response: We have revised this statement in the revised version.See lines 64-65 in the revised version.

Original sentence: Metals can be accumulated in plant leaves through foliar transfer after deposition of atmospheric particles on the leaf surfaces.

Modify the sentence: After atmospheric particles are deposited on the surface of plant leaves, heavy metal elements can be transferred and accumulated in plant leaves. 

Question 4: Line 80-81: Revise sentence.

Our response: We have revised this statement in the revised version. See lines 89-92 in the revised version.

Original sentence: It has a high proportion of secondary industries, among which heavy industries, such as automobile manufacturing, nonferrous metal smelting, special equipment manufacturing, and railway transportation equipment manufacturing, are most common.

Modify the sentence: The proportion of secondary industry is high, among which automobile manufacturing, non-ferrous metal smelting, special equipment manufacturing and railway transport equipment manufacturing and other heavy industries account for a large proportion.

Question 5: Line 116-117: Plant leaves were washed before drying? How if suspended particles were still trapped on surface instead of inside leaves?

Our response: In order to detect as much heavy metals as possible on the surface and inside of the leaves, the collected leaves were not cleaned in the study, they were dried directly. See lines 135-137 in the revised version.

Question 6: Line 130: What and how the measurement method edited?

Our response: According to the operation regulation of ICP-MS instrument, the flow rate of atomizer is 0.8lL/min, the auxiliary gas flow rate is 1.2L/min, the RF power of ICP is 1200W and the lens voltage is 1.2V. After the instrument is stable, the standard working solution is determined by adding the internal standard working solution on line using the internal standard Quantitative analysis method. Taking the concentration of 5 elements as the abscissa and the strength ratio of 5 elements to the corresponding internal standard elements as the ordinate, the standard curve is drawn and the regression equation is calculated, then, the reagent blank solution and the processed sample solution are respectively introduced into the instrument atomizer for determination. The strength ratios of 5 elements and corresponding internal standard elements were substituted into the regression equation, and the contents of 5 elements in the sample were obtained.

Question 7: Line 189: Spelling mistake  

Our response: The error Significant has been changed to Significant after checking.

Question 8: Line 191: Write heights in ascending order and double check which one is correct line 191 or mentioned in abstract?

Our response: Thank you very much for your suggestion. We have revised the summary in the revised version. See lines 24 in the revised version.

Question 9: C. deodara values missing in Table 2? 

Our response: Thank you very much for your question. We have revised Table 2 in the revised version. See lines 224 in the revised version.

Question 10: Why Ni and Cu showed higher values in campus plant leaves in O. japonicus and lower roadside leaves and also in Nov?

Our response: On campus, because O. japonicus was planted just before sampling in May, its leaves were contaminated with soil, resulting in higher levels of Ni and Cu in the leaves, therefore the concentrations of Ni and Cu in plant leaves were higher. In November, soil on plant leaves is washed away by the rainy season, reducing nickel and copper levels.

Question 11: how can plant leaves directly affect the human and ecology?

Our response: They can directly adsorb, block, and filter atmospheric heavy metal pollutants through leaf surface structures, such as leaf morphology, leaf insertion angle, surface secretion, and surface roughness, reducing the amount of dust in the air and effectively purifying the latter. See lines 53-56 in the revised version.

Question 12: Effect of rain and growing period of plant leaves required more discussion.

Our response: The time of collecting sample was chosen in mid-May and mid-November in order to avoid the influence of plant growth period. The adsorption ability of leaves to heavy metal elements is unstable during the growth period. The sampling was carried out after two weeks of no precipitation in the month in order to avoid the influence of rain erosion on the concentration of heavy metal elements on the surface of plant leaves.

We have added a description to the revised version, see lines 126-130 on page 3 of the revised version.

In this study, the contents of heavy metal elements absorbed by plant leaves during growing period were studied to analyze urban pollution. Therefore, we are mainly concerned about the ability of plant leaves to absorb heavy metal elements. In the next phase of the study, we plan to study the fluctuation of heavy metal concentrations in plant leaves from the physiological point of view.

 

References

1. LI Shao，Huayun Xiao, D.W., Congguo Tang. Review on Research on Traffic-Related Heavy Metals Pollution. Earth and Environment 2012, 40, 445-459, doi:10.14050/j.cnki.1672-9250.2012.03.016.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Zhang et al examined the concentrations of heavy metals in plants leaves across the city of Baoji and derived a time and space distribution of heavy metals that can help to inform the level of urban pollution. Overall the study is well designed and the writing is well organized. The content of the paper also fits quite well with the journal and the content and methodology introduced in the paper will attract a broad audience who focus on urban pollution measurement with low-cost techniques. However, I do have some questions with the data presented in this work as insufficient information was provided by the authors regarding data variance and overall trend.  

The author mentioned that the variation coefficient of 80 % samples was more than 0.3. It would be easier to compare if the authors could show the variations together with mean values in the tables. Although as the author discussed later in the text, there are many reasons that can cause the variations such as rainfall, it is still important to carefully examine the variance between samples to show the results and conclusions drawn from the results are valid. Maybe I misread the text but it seemed that at least four samples were taken at each site - how do these samples agree with each other? Since with these samples collected at the same time, the impact of environmental factors should be minimal. 

The paper may only be considered for publication after the above concern is addressed.

 

Author Response

Question 1: However, I do have some questions with the data presented in this work as insufficient information was provided by the authors regarding data variance and overall trend.  The author mentioned that the variation coefficient of 80 % samples was more than 0.3. It would be easier to compare if the authors could show the variations together with mean values in the tables.

Our response: The CV and mean values of the heavy metals in the samples have been modified in this revision. See lines 224 in the revised version.

Table 2. Mean element concentration, coefficient of variation (CV) of roadside plant leaves in Baoji

			Ni (mg·kg-1)		Cu (mg·kg-1)		Cd (mg·kg-1)		Pb (mg·kg-1)		Zn (mg·kg-1)
Species	Time		Mean	CV	Mean	CV	Mean	CV	Mean	CV	Mean	CV
O.japonicus (I)		May	3.07	0.45	10.57	0.30	0.40	0.88	10.60	1.15	67.49	0.35
		Nov.	3.07	0.44	13.71	0.25	0.23	0.45	4.74	1.73	52.43	0.45
L. vicaryi (II)		May	2.55	0.45	10.65	0.57	0.32	1.42	5.00	0.95	69.31	0.39
		Nov.	4.39	0.39	15.20	0.34	0.18	0.77	8.05	0.66	63.82	0.44
L. vicaryi (III)		May	1.92	0.28	8.63	0.38	0.21	0.78	3.71	0.58	56.79	0.19
		Nov.	1.79	0.47	12.73	0.29	0.12	0.57	4.67	0.55	52.49	0.42
P. acerifolia (IV)		May	3.48	0.19	13.61	0.32	0.21	0.59	9.78	0.60	65.51	0.34
		Nov.	3.79	1.05	8.56	1.06	0.09	1.56	3.41	1.56	47.69	0.77
S. japonica (IV)		May	2.52	0.21	10.41	0.31	0.11	0.34	7.17	0.45	57.69	0.23
		Nov.	11.55	0.89	14.03	0.19	0.22	0.15	11.37	0.37	73.82	0.07
C. deodara (IV)		May	3.08	0.98	7.25	0.66	0.19	0.46	30.28	1.47	85.43	0.74
		Nov.	1.73	0.12	8.38	0.51	0.13	0.77	4.19	0.03	29.65	0.55

 

Question 2: How do these samples agree with each other? Since with these samples collected at the same time, the impact of environmental factors should be minimal.

Our response: In order to obtain the data of heavy metal pollution concentration in different height, we select four layers in each station to collect samples. At the same time, to reduce the error, GPS was used to collect leaf samples from each layer due east, due west, due south and due north.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article "Spatiotemporal differences and ecological risk assessment of heavy 2 metal pollution of roadside plant leaves in Baoji City, China" deals with a very important topic of accumulation of pollutants on the surface of plants, as well as sorption inside the cells.The article has been structured correctly.However, some aspects need to be clarified / improved:

1. I propose to strengthen the introduction with the following literature items:

Jang, B.-K.; Park, K.; Lee, S.Y.; Lee, H.; Yeon, S.H.; Ji, B.; Lee, C.H.; Cho, J.-S. Screening of Particulate Matter Reduction Ability of 21 Indigenous Korean Evergreen Species for Indoor Use. Int. J. Environ. Res. Public Health 2021, 18, 9803. https://doi.org/10.3390/ijerph18189803

Cichowicz, R.; Dobrzański, M. 2021. Modeling Pollutant Emissions: Influence of Two Heat and Power Plants on Urban Air Quality. Energies 2021, 14, 5218. https://doi.org/10.3390/en14175218

Mohsen, M.; Ahmed, B.M.; Zhou, J.L. Particulate matter concentrations and heavy metal contamination levels in the railway transport system of Sydney, Australia. Transportation Research Part D: Transport and Environment. Vol. 62, 2018, Pages 112-124. https://doi.org/10.1016/j.trd.2018.02.015.

Obolkin, V.; Khodzher, T.; Sorokovikova, L.; Tomberg, I.; Netsvetaeva, O.; Golobokova, L. (2016) Effect of long-range transport of sulphur and nitrogen oxides from large coal power plants on acidification of river waters in the Baikal region, East Siberia, International Journal of Environmental Studies, 73:3, 452-461, DOI: 10.1080/00207233.2016.1165481

2. Please clarify whether the samples were taken only on one day of a specific month? Does it mean that the measurements were not repeated in order to check or average the obtained results for a given month?

3. I believe that the potential of Figure 3 has not been used. It would be possible to present the pollution dispersion maps in the city background to better indicate locations with increased concentrations of heavy metals.
4. The summary lacks information on the possibility of using the measurement methodology for other locations.

Author Response

Question 1: I propose to strengthen the introduction with the following literature items:

Jang, B.-K.; Park, K.; Lee, S.Y.; Lee, H.; Yeon, S.H.; Ji, B.; Lee, C.H.; Cho, J.-S. Screening of Particulate Matter Reduction Ability of 21 Indigenous Korean Evergreen Species for Indoor Use. Int. J. Environ. Res. Public Health 2021, 18, 9803. https://doi.org/10.3390/ijerph18189803

Cichowicz, R.; Dobrzański, M. 2021. Modeling Pollutant Emissions: Influence of Two Heat and Power Plants on Urban Air Quality. Energies 2021, 14, 5218. https://doi.org/10.3390/en14175218

Mohsen, M.; Ahmed, B.M.; Zhou, J.L. Particulate matter concentrations and heavy metal contamination levels in the railway transport system of Sydney, Australia. Transportation Research Part D: Transport and Environment. Vol. 62, 2018, Pages 112-124. https://doi.org/10.1016/j.trd.2018.02.015.

Obolkin, V.; Khodzher, T.; Sorokovikova, L.; Tomberg, I.; Netsvetaeva, O.; Golobokova, L. (2016) Effect of long-range transport of sulphur and nitrogen oxides from large coal power plants on acidification of river waters in the Baikal region, East Siberia, International Journal of Environmental Studies, 73:3, 452-461, DOI: 10.1080/00207233.2016.1165481

Our response: Thank you very much for the papers you recommended for us, we read these articles carefully, and added relevant content in the article, so that our scientific paper further improved.

Articles such as Jang and Obolkin are cited in line 33 on page 1 of the revision; articles such as Cichowicz are cited in line 47 on page 2 of the revision. Mohsen et al paper is quoted by us on page 9, line 291 of the revised manuscript.

Question 2: Please clarify whether the samples were taken only on one day of a specific month? Does it mean that the measurements were not repeated in order to check or average the obtained results for a given month?

Our response: Our samples were collected in mid-May 2017 and mid-November 2017, and the sampling time was chosen to be the period without rainfall two weeks ago. May is the beginning of the growth of vegetation leaves, November vegetation leaves have been mature but have not fallen, is a full cycle of leaf growth, so we choose to collect leaves in these two months. Leaves from the two periods were compared to observe changes in leaf accumulation of heavy metals. We investigated the heavy metal pollution in the main streets of Baoji by studying the concentration of heavy metals in the leaves, the purpose of this study was not to investigate the fluctuation of the ability of plant leaves to absorb heavy metals during growth.

Question 3: I believe that the potential of Figure 3 has not been used. It would be possible to present the pollution dispersion maps in the city background to better indicate locations with increased concentrations of heavy metals.

Our response: Thank you for your suggestion, we added a new graph (figure 4) in the revised version, it is the time-space kriging of heavy metal pollution concentration.See lines 373 in the revised version.

Question 4: The summary lacks information on the possibility of using the measurement methodology for other locations.

Our response: Thank you very much for your suggestion, we have added in the introduction to other areas using related techniques to study urban pollution using plant leaves. See lines 73-87 in the revised version.

Based on the analysis of common greening tree species in Beijing area, it is concluded that Sophora japonica L. and Platycladus orientalis L. have strong enrichment ability to Cr and PB, and the heavy metal content is strongly correlated with the heavy metal pollution degree in leaves[2,3]. Based on the analysis of metal contents in the leaves of greening plants along a traffic route in Lanzhou and their correlation, it was found that there were significant differences in heavy metal contents in plants in different road environments[4]. Some scholars through the city of 23 plant leaf research findings Buxus sinica, Buxus megistophylla, Prunus cerasifera, and Ligustrum×vicaryi were the most effective plant species for accumulating particles[5].

 

References

1. LI Shao，Huayun Xiao, D.W., Congguo Tang. Review on Research on Traffic-Related Heavy Metals Pollution. Earth and Environment 2012, 40, 445-459, doi:10.14050/j.cnki.1672-9250.2012.03.016.
2. Shuxin Fan, Y.C., Li Dong. Dust absorption capacities of eight evergreen broad-leaved plants in Beijing,China. Chinese Journal of Applied Ecology 2017, 28, 408-414, doi:10.13287/j.1001-9332.201702.021.
3. Shaoning Li, L.K., Shaowei Lu, Bo Chen, Chen Gao, Yuan Shi. Beijing Common Green Tree Leaves' Accumulation Capacity for Heavy Metals. Environmental Science and Pollution Research 2014, 35, 1891-1900, doi:10.13227/j.hjkx.2014.05.037.
4. Jing Li, Y.X., Guiying Li, Gongli Feng, Xiaoli Jiang, Lianbang Si, Yingli Yang. Analyses of Heavy Metal Accumulation and Physiological Characteristics in Leaves of Main Arbor and Shrub Plants in Traffic Roads of Lanzhou City. Ecology and Environmental Sciences 2019, 28, 999-1006, doi:10.16258/j.cnki.1674-5906.2019.05.017.
5. Chen, H.; Xia, D.-s.; Wang, B.; Liu, H.; Ma, X. Pollution monitoring using the leaf-deposited particulates and magnetism of the leaves of 23 plant species in a semi-arid city, Northwest China. Environmental Science and Pollution Research 2022, doi:10.1007/s11356-021-16686-1.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Previous concerns were addressed by authors.

Author Response

thanks