Edinburgh
Prof John Farmer
Science of the Total Environment
Murchison House
West Mains Road
Edinburgh
United Kingdom
EH9 3LA
Telephone +44(0)131 6671000
Direct Line +44(0)131 6500389
Main Fax +44(0)131 6682683
E-mail amm@bgs.ac.uk
2nd February 2010
Dear Prof Farmer,
Thanks for the prompt and supportive comments on the manuscript. We have amended the
manuscript slightly in response to the reviewers’ comments, and resubmitted as directed.
Below is a detailed response to the reviewer’s comments. We hope the responses satisfy the
queries.
Please get in touch is you have any more queries
Dr Alan MacDonald
Principal Hydrogeologist
Reviewer #1: This is a very good paper that I strongly recommended for
publication.
Thanks for the compliment
However, I have a few comments. In general, I think that the health focus
feels a bit "thrown in" to make the findings interesting. The levels measured
in this study are mainly well below any levels found to exert any adverse
health effects, and also the paper is interesting without getting in to the
health issue too much. Although the current WHO guideline may well be set too
high, the interesting findings of this paper is rather the hydro- and
geochemical bit of it. So perhaps it is more appropriate to only mention the
health concerns related to Mn exposure without getting in to too much detail?
For most of us, uptake of Mn from drinking water is well regulated by our
bodies. Also, when levels are too high, we usually choose not to drink it (if
there is an alternative, which I assume there usually is in Scotland),
because it tastes and smells strange (hence the aesthetic guideline values
set).
There appears to be growing evidence that Mn at small concentrations could be
harmful to health. Our study found 9% of sites to be greater than the existing
WHO guideline value of 0.4 mg/l. Our concern in the paper is mainly due to
private water supplies which are generally poorly regulated worldwide, and often
used because alternatives are expensive or unavailable. Therefore we believe
the health angle is justified. However, we have taken these comments onboard
and softened the health element (see responses below)
The paper would greatly benefit from focussing the discussion and conclusions
on the factors controlling Mn concentrations. What implications these findings
may have on monitoring with regard to water Mn variability? You found large
differences both between and within aquifers, which makes me wonder about
variations in time. Is it really appropriate to sample once and assume the
concentration measured is what the ground water holds at any given time? With
regard to its apparent correlation with Fe, are there any specfic rocks in
which it is likely to find elevated Mn? I think a discussion of these issues
would be very interesting to many readers.
As recommended we have extended the monitoring section in the discussion to
address these issues: we have added in a discussion of the use of rock
geochemistry for predicting Mn, and also the requirement for better sampling
protocol, including time variant sampling.
Revised section:
Section 4.4
The research results have particular implications for monitoring of private water supplies in
Scotland, which are often groundwater based. Water quality standards for private supplies in
Scotland are derived from EC regulation, and monitoring and protection is carried out by
local authorities. The level of monitoring depends on whether a private water supply is
classified as Type A (providing 10 m3 or more per day, supplying 50 or more people, or used
for commercial or public activity) or Type B supplies (all others) (Astron, 2006). Chemical
parameters are tested for in both types of supply, but Type A supplies are subject to more
regular and stringent testing and enforcement of water quality regulations than Type B, which
are only monitored on a discretionary basis (Donnelley, 2008). Therefore, Mn may not be
tested and high concentrations can go undetected.
Another major issue is sampling protocol. Samples collected for routine monitoring carried
out by the regulatory bodies are often not filtered or acidified in the field, giving unreliable
Mn data. In creating the dataset used for this Scottish study, a comparison was undertaken
between samples collected with good and poor protocol for 40 locations. For samples with
poor field protocol Mn concentrations were consistently underestimated by more than an
order of magnitude. For a reliable measure of exposure to Mn for public health reasons,
samples would need to be taken throughout the year to capture natural variations.
The range of Mn concentrations encountered in each geological unit also has implications for
groundwater monitoring. Manganese concentrations in excess of the Scottish limit of 0.05
mg l-1 and the WHO health guideline value of 0.4 mg l-1 were found in each aquifer unit, and
there was more variability within each unit than between them. Therefore, developing hazard
maps identifying areas of potential elevated Mn concentrations from geology alone are
unlikely to be effective. Monitoring therefore needs to be widespread.
Based on the discussion above, more widespread testing of Scottish private water supplies
using appropriate sampling protocols is required to give greater confidence in the Mn
concentrations in private water supplies in Scotland. These recommendations have relevance
elsewhere. Although studies in other countries have reported elevated Mn concentrations in
groundwater-sourced drinking water supplies, monitoring of drinking water supplies for Mn is
not routine.
More specifically, I have the following comments:
Line 61: One gets the impression that adverse health effects can occur if
exposed to drinking water containing between 0.004-3.91 mg/L. This sentence
should perhaps therefore be rephrased to clarify at which levels adverse
effects were found.
Revised section:
For example, Wasserman et al. (2006) identified a significant negative relationship between
well water Mn concentration (0.004-3.91 mg l-1) and measures of intellectual function in 142
children of 10 years of age in Bangladesh (notable difference in intellectual function between
<0.2 mg l-1 group and > 1 mg l-1 group).
Line 68, same comment as above. However, I think it is good that the reader
gets an idea at which concentrations Mn is considered unsafe, so the values
should not be excluded.
Revised section:
In a study in Greece (Kondakis et al., 1989), neurological symptoms of chronic Mn poisoning
were found to increase with exposure to Mn from groundwater-sourced water supplies in
three populations of adults with similar social and dietary characteristics who had been living
in the same area for at least 10 years (concentrations ranging from 0.0036 to 2.3 mg l-l, effects
were first noted in a group drinking concentrations 0.08 to 0.25 mg l-l).
Line 74: The Swedish GV is technical/aesthetic and not health-based, not sure
about the US but I think it's the same.
We have removed the Swedish GV and clarified that the WHO and US GVs are
for health reasons not aesthetic
Line 78-82: The sentence says that Bouchard recommends..., but is then
referenced to Ljung and Vahter. Please clarify.
We have made this section clearer:
In the studies by Wasserman et al. (2006) and Kondakis et al. (1989) there was evidence of a
dose-response relationship between the severity of neurotoxic effects and exposure to Mn in
well water suggesting that exposure to Mn concentrations below the WHO guideline value
could still result in adverse health effects, with children most vulnerable (Ljung and Vahter,
2007). Consequently Bouchard et al. (2007) recommend that further research is required to
establish adequate guidelines for Mn in drinking water.
Line 97: in addition to mobilisation, microorganisms also have an effect on Mn
immobilisation. Although "mobilsiation" entails both, it's probably good to
clarify that they can actually decrease the soluble concentration in water.
We have made this more explicit:
Micro-organisms can play an important role in Mn mobilisation in the
environment and can both enhance or inhibit concentrations in groundwater.
The effects can be direct, through enzymatic catalysis of Mn oxidation and
reduction and specific binding by cell-associated materials, or indirect, by
altering the pH and Eh conditions of the micro-environment, thereby
influencing Mn speciation and concentration (Nealson, 1983).
Line 110-111: In combination with previous elaborations on health effects,
"increasing concerns.. in excess of drinking water supply limit" sounds like
there may be a serious health issue with the Scottish ground water, which is
not the case. I assume that the 50 µg/L limit value is set for technical and
not health reasons. It is therefore a bit dubious to link health concerns
(line 116) to exceedance of Mn concentrations of 50 µg/L. Again, health
concerns should not really be a focus in this paper, but rather the hydro- and
geochemistry.
We have changed the emphasis of this section to be less alarmist:
There is increasing evidence (Robins, 2002; MacDonald and Ó Dochartaigh, 2005) that Mn is
often present in Scottish groundwater at concentrations in excess of the Scottish drinking
water supply limit of 0.05 mg l-1(as defined by the Water Supply (Water Quality)(Scotland)
Act 2001) and may be in excess of the WHO guideline value of 0.4 mg l-1.
Section 4.4: The reasoning in this section seems to depend on the assumption
that authorities may exclude some paramers in water testing to reduce costs,
and that this parameter may be Mn. How likely is this to happen? I think you
need to clarify this section in order to make your point, because at present
it seems a bit far-fetched. And also, only 9% of the wells had concntrations
above WHO's guideline value. Consumption of drinking water above this
concentration is mainly a risk for infants receiving formula (uptake is
regulated in children and adults), so the concern for excessive intake from
this reasoning can seem a bit exaggerated.
See responses above in general section, and our expanded monitoring section.
We have emphasised that the main problem is for private water supplies where
monitoring is limited. For many parts of the world, private water supplies form a
much greater proportion of the water supply and the number of people affected
will be much greater. The 9% above current WHO GV is potentially a health
issue for children and adults alike. This is why we have a short discussion on the
health studies which indicate the potential neurological effects on adults at low
doses.
Reviewer #2: This is a high quality, extremely well-written paper, presenting
a comprehensive dataset. The data have been rigorously analysed, and
conclusions are clearly based on the data presented. The paper should be of
wide international interest, and can be accepted in its present form.
Great!