Assessment of the Impacts of Anthropogenic Activities on a Large River Using Longfin Eel as a Bioindicator

Round 1

Reviewer 1 Report

The aim of this study is clear. The authors investigated site-specific responses of Longfin Eel as a bioindicator. The title is informative and relevant, and most references are relevant and recent. The authors introduced the importance of the sites studied and pointed out eels have been recognized as bioindicators for several kinds of contaminants. The research questions were clearly outlined.

Major comment:

L208-209: “Chemical analyses of PCBs, organochlorines, and PAHs were not carried out in eel sampled during summer since no chemical was detected in sediments.” Eel lives both in sediment and water, is there any data collected from water to justify this decision?

Minor comments:

1. Table 4: what method was used to determine TOC?

2. L297: “…for the resident eels at Piano Flat in Summer statistically different (P<0.05) from the others.” It would be better to mark significant difference values in the table.

3. Table 7: It is better to place the title above the table.

Author Response

Reviewer 1:

Comments and Suggestions for Authors

The aim of this study is clear. The authors investigated site-specific responses of Longfin Eel as a bioindicator. The title is informative and relevant, and most references are relevant and recent. The authors introduced the importance of the sites studied and pointed out eels have been recognized as bioindicators for several kinds of contaminants. The research questions were clearly outlined.

Reply: Thank you for these positive comments.

Major comment:

L208-209: “Chemical analyses of PCBs, organochlorines, and PAHs were not carried out in eel sampled during summer since no chemical was detected in sediments.” Eel lives both in sediment and water, is there any data collected from water to justify this decision?

Reply: Water samples were not collected for the analysis of PCBs, organochlorines, and PAHs due to the hydrogeological properties of the Mataura River and nature of the anthropogenic inputs. The absence of significant industries that produce effluent specifically containing PCBs, organochlorines, and PAHs, together with a combination of high water flows and flow volumes in the Mataura River, results in significant dilution factors for identifiable anthropogenic inputs into the Mataura River. Some of these anthropogenic inputs (stormwater from roading and urban surfaces) are associated with heavy rainfall events during which the dilution factors increase considerably. After considering these factors, it was apparent we were highly unlikely to be able to detect the diluted ultra-trace level concentrations of PCBs, organochlorines, and PAHs in the water of the Mataura River. The hydrophobic properties of PCBs, organochlorines, and PAHs are such that they preferentially partition to and accumulate within the organic carbon of sediments within aquatic ecosystems. Through this process sediments effectively act as a passive sampling medium for hydrophobic POPs including PCBs, organochlorines, and PAHs. Over time trace residues of these POPs in the water of the Mataura River continue to accumulate within the sediment in the riverbed. Therefore, we sampled and analysed PCBs, organochlorines, and PAHs in the sediments of the Mataura River to obtain a measure of the extent to which these POPs prevailed within the Mataura River catchment.

Minor comments:

1. Table 4: what method was used to determine TOC?

Reply: The following paragraph was added to the manuscript:

Sediments were dried to a constant weight at 105^oC, pre-treated with acid to remove inorganic carbonates, and total organic carbon determined by elemental analysis (Elementar Combustion Analyser).

2. L297: “…for the resident eels at Piano Flat in Summer statistically different (P<0.05) from the others.” It would be better to mark significant difference values in the table.

Reply: Asterisks have been added to the table

3. Table 7: It is better to place the title above the table.

Reply: Caption moved to top

Reviewer 2 Report

Dear Editor,

Manuscript by Olivier Champeau et al. “Assessment of the Impacts of Anthropogenic Activities on a Large River Using Longfin Eel as a Bioindicator” is describing possible effect which might occur in areas, polluted with POPs by using caged A. dieffenbachia, as a sensitive model fish to POPs exposure, in in situ study. Chemical analyses of sediments and fish was performed within measuring three biochemical biomarkers, which are recognized markers of presence of PAH, detoxification and oxidative stress. Additionaly, this study showing seasonal effect on presence of POPs and on biomarker activity. Manuscript is easy to read and follow main results.

Just few minor comments:

1. Line 260 double dots
2. Line 87-88 ()

Major comment.

In this study eels have EROD activity units mom/min/mg of protein. Does author sure that activity in mol? And not pmop or nmol? Since EROD activity was measured in post mitochondrial supernatant (not microsomes, which are rich on phase I enzymes as CYP1A (catalytic activity EROD)), activity of EROD shoud be less. For example EROD activity in pigs is in range 20-400 pmol (depends from specie). Fish with such high EROD activity must be mutants.

TBARS units is nmol/mg of protein. In the method, part authors wrote that post mitochondrial fraction was used to study. In cited reference microsomal lipid peroxidation is described. If authors modified something, it should be noted in brief method description.

Does presence of POPs in fish tissue correlate with biomarkers? Clarify please.

Authors should revise manuscript before submitting again reviewing, mainly, the sections Materials and methods, Results, and Discussion.

Author Response

Reviewer 2:

Dear Editor,

Manuscript by Olivier Champeau et al. “Assessment of the Impacts of Anthropogenic Activities on a Large River Using Longfin Eel as a Bioindicator” is describing possible effect which might occur in areas, polluted with POPs by using caged A. dieffenbachia, as a sensitive model fish to POPs exposure, in in situ study. Chemical analyses of sediments and fish was performed within measuring three biochemical biomarkers, which are recognized markers of presence of PAH, detoxification and oxidative stress. Additionaly, this study showing seasonal effect on presence of POPs and on biomarker activity. Manuscript is easy to read and follow main results.

Reply:

Just few minor comments:

1. Line 260 double dots

Reply: Removed supplementary dot.

 

1. Line 87-88 ()

Reply: Added closing parenthesis.

 

Major comment.

In this study eels have EROD activity units mom/min/mg of protein. Does author sure that activity in mol? And not pmop or nmol? Since EROD activity was measured in post mitochondrial supernatant (not microsomes, which are rich on phase I enzymes as CYP1A (catalytic activity EROD)), activity of EROD shoud be less. For example EROD activity in pigs is in range 20-400 pmol (depends from specie). Fish with such high EROD activity must be mutants.

Reply: Unit is in nanomole. Figures have been corrected accordingly.

TBARS units is nmol/mg of protein. In the method, part authors wrote that post mitochondrial fraction was used to study. In cited reference microsomal lipid peroxidation is described. If authors modified something, it should be noted in brief method description.

Reply: A reference to the paper with the method used has been added to the manuscript

Does presence of POPs in fish tissue correlate with biomarkers? Clarify please.

Reply: We have clarified the analytical data by including the following sentence in the Discussion section: “There was no correlation between the sum of DDT congeners and the EROD response which suggest that the fish may be exposed to other inducers likely found in the water column. It is important to use both bioaccumulation and biomarker response data in environmental risk assessment frameworks (van der Oost 2003).”

Authors should revise manuscript before submitting again reviewing, mainly, the sections Materials and methods, Results, and Discussion.

Reply: The manuscript was edited by Gretchen Rasch (Cawthron Institute) who provided further editorial comments- we have inserted her details in the Acknowledgements section.

Round 2

Reviewer 2 Report

Dear Editor,                                                                                        25/9/2020

Please find below my comments on Manuscript entitled „Assessment of the Impacts of Anthropogenic Activities on a Large River Using Longfin Eel as Bioindicator”. Second revision.

Authors replied on my comments. However, it is unbelievable that Anguilla dieffenbachii has EROD 40 nmol/mg/min activity in postmitahondrial supernatant. For such high activity CYP1A1 should be present in high quantities together with other CYPs. Measure total CYP content in the samples.

In article Responces of Sortfin Eel (Anguilla Australis) exposed in situ to pulp and paper effluent, EROD activity was in 0.1-0.3 pmol/mg/min range. 

Please, check your resorufin standard curve calculation.

Author Response

Please see the attachment 

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

I have no further comments.