Bioaccumulation of Trace Metals in Groenlandia densa Plant Reintroduced in Western Pomerania

Round 1

Reviewer 1 Report

The ms by Podlasinska et al. reports the accumulation of heavy metals by the endangered and re-introduced aquatic plant species Groenlandia densa to north-western Poland. Material has been collected from three distinct sites with various anthropogenic contamination. The plants show a distinction by metal type as well as a selective accumulation when the metal is offered by the sediment or the water.

General points:

• The authors talk about the reintroduction of G. densa to the respective areas. When was this re-introduction performed? Was it done at the same time for all investigated sites? In other words, for how long are these G. densa populations exposed to the contamination before sampling?
• The results show differentiated accumulation of metals to the plant parts. What is the idea for the storage/attachment/incorporation of the metals in the plant? Adsorption to the cell wall, true uptake, homeostasis mechanisms? Any signs of programmed cell death or growth restrictions due to metal contamination? Please comment.
• Is there any idea for the composition/amounts of the metals tested and where the contamination is resulting from, e.g. why Cd, Cu, Zn and Mn is fairly high whereas Hg is low in site I? Also, why is the Mn value that high in site III? Table 4: Site II, Mn value for “sediment”: should that comma be a full stop and read 49.921 (it is 49,921 in the table)?
• Figures & Tables:

Figure 1: small inlay showing a – d: indicate the meaning of these letters in the figure caption.

Figure 2: units need to be included.

Figure 3 mark with them A and B and relate to the respective parts with BCF G/S and BCF G/W in the caption.

Page 9, line 282ff (Fig. 3): It is stated that for the examined metals, most BCF G/S values are below 1 (apparently Fig. 3 a, apart from Cd, Cu and Zn). The BCF G/W values are similar for these elements although there are differences in the sites, particularly for copper and zinc. Please, comment. Also, Mn seems to be accumulated only when applied by water, not by the substrate. Can authors elaborate a bit more on these results, please. In line 289, it is stated: ”This condition was met by Groenlandia for manganese, zinc and copper.” But what about Cd? The Cd values for BCF G/W are above 10000; or is it a typo and it should read cadmium instead of copper in line 289; and the legend in Fig 3 b is incorrect by a factor 10 (thus should be 500 – 3000, instead of 5000 to 30 000)?

Table 7 (line 304): N=2 is very low; please include a statement why not more data have been collected here. Authors only focus on two significant coefficients witin this table but some other numbers are almost as high (e.g. Cd with both, leaf blade length and width)

• Conclusions

There are inconsistencies with the spelling of Groenlandia: GRD in line 307, GD in line 311; in all the rest of the text, it is referred to as G. densa and I suggest to stick to the latter throughout the text. Parts of the conclusion are redundant with the abstract.

• Minor points:

Line 313: “in” appears doubled

Line 161: “index” appears doubled

Author Response

Thank you very much for your careful review of our manuscript, valuable comments and suggestions sent to us.

The re-introduction was performed in September 2017 at Site 1 and in June 2018 at sites 2 and 3. There was about 10 months time difference between re-introduction between site 1 and sites 2 and 3. The  Site 1 – Chwalimski Potok was the place of reproduction and breeding of G.densa specimens  from which plants were taken for further reintroduction at selected sites. Prior to initial sampling in 2017 G. densa had been exposed to discussed contaminants for about  2- 2.5 years.

As there are no available results about metabolic mechanisms of metal accumulation in G.densa we devised a simple test to check accumulation of metals in different plant parts. We assumed that the adsorption to the cell wall and true uptake are predominant pathways of heavy metals storage. No macroscopic signs of cell damage as well as growth restrictions were observed. We would like to investigate this issue in further research.

The contamination differs between experimental sites primarily due to different sources (agricultural, urban and forest) and pollutant loads. At site 1 the amount of Cd, Cu, Zn and Mn is fairly high whereas Hg level is low due to natural background occurrence. G. densa occurs naturally in post glacial areas where groundwater in confined aquifers, which is high in Mn and Fe, inflows into surface water, which creates favorable conditions for this species.

We added requested information to Fig. 1-3 according to your suggestion.

Thank you very much for your comment to: Page 9, line 282ff (Fig. 3): It is stated that for the examined metals, most BCF G/S values are below 1 (apparently Fig. 3 a, apart from Cd, Cu and Zn). The BCF G/W values are similar for these elements although there are differences between the sites, particularly for copper and zinc. It is probably due to different sources of pollution. Unfortunately, we didn’t investigate the amount of heavy metals in water on the regular basis, we only sampled once. Hence it is difficult to interpret the results correctly and without errors in interpretation.

Thank you very much for your comment to: In line 289, it is stated: ”This condition was met by Groenlandia for manganese, zinc and copper.” It should be Cadmium.  The legend is a proper one.

Your comment on Mn accumulation when applied by water is very accurate. We elaborated a bit more on these results.

There was no possibility to collect more data, the amount and the size of samples was limited by the consent given by The General Director for Environmental Protection. We focused on two significant coefficients because only them were statistically proved. 

We corrected the spelling of Groenlandia densa according to your suggestion. We removed conclusions from abstract. 

Double words were removed.

Reviewer 2 Report

It is an interesting study realted to environment bioremediation.

1. Please avoid the use of abbreviations in the Abstact, and introduce it in the Introduction
2. The name of the plant need to be written in italic
3. Information about geochemical index from Section 2.3 need to be moved to Section 2.4.
4. Check carefully text  for repetions of words
5. In Table 5 include values for Igeo and CF as well as Maximum permisible levels
6. Which site was considered as contol? If site I why?
7. Line 234 "mean values of 243the investigated elements were found at site II" what kind of mean values?
8. Lines 250-261 how can you compare you data with control data reported in other studies?

Author Response

Thank you very much for your careful review of our work and suggestions for changes in the manuscript.

1. All abbreviations form Abstract have been removed.
2. We used italic to write the name of plant.
3. Information about geochemical index from Section 2.3 has been moved to Section 2.4.
4. Repetitions of words from text have been removed.
5. Igeo and CF and ecotoxicological criteria indices were added to the value table. The Maximum permissible levels are not included because there are no clear values for the Maximum Permissible Levels in Polish legislation. There was a regulation according to which it was possible to assess whether the spoil (including bottom sediment) was contaminated (Regulation of the Minister of the Environment of April 16, 2002 on the type and concentration of substances that make the spoil contaminated (Journal of Laws of 2002, No. 55, item 498)). Unfortunately, it has been repealed and there is no valid regulation concerning this problem. On the other hand according to Regulation of the Minister of Climate of January 2, 2020 on the waste catalog (Journal of Laws 2020 item 10; Rozporządzenia Ministra Klimatu z dnia 2 stycznia 2020 r. w sprawie katalogu odpadów, Dz.U. 2020 poz. 10)  bottom sediments can be treated as hazardous or non-hazardous waste. According to the conditions set out in this legal act, bottom sediments from investigated watercourses should be classified as non-hazardous waste.
6. The first site (Site1) was treated as control. The main reason for this was that this site was reintroduced first and was the nursery of plants for the reintroduction of other plants.
7. The expression in Line 234 "mean values of the investigated elements were found at site II" was used to indicate that these values were not the lowest and highest ones within the range.
8. As we didn’t apply artificial pollution and Groenlandia densa plants were taken from natural stands we compared them with control plants from other studies as they were also without any additional treatment.

Round 2

Reviewer 2 Report

Dear authors, thank you for considering my reccomendations!