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Environmental
Science
Water Research & Technology
PAPER
Cite this: DOI: 10.1039/c8ew00890f
Received 30th November 2018,
Accepted 26th January 2019
DOI: 10.1039/c8ew00890f
rsc.li/es-water
Effectiveness of a copper based molluscicide for
controlling Dreissena adults
Ian Lake-Thompson*and Ron Hofmann
Pilot scale experiments were conducted to test the copper-based EarthTec QZ molluscicide for killing
adult quagga mussels. The work was done in Lake Ontario water with average water temperatures ranging
between 6.7–10.4 °C. Trials consisted of eight copper concentrations varying between 30–500 μgL
−1
in
triplicate under continuous and cyclical flow regimes. A 1 mg L
−1
total chlorine trial was used to provide a
comparative standard. Complete control was achieved in all test groups ranging within 7 to 28 days for the
copper trials, while the chlorination group required 41 days. The efficacy of the copper product was not
impacted by continuous versus cyclical flow regime. Results from this study indicate that the copper based
product is a viable molluscicide option for adult control with possible advantages over chlorine in cyclical
flow regimes and at colder water temperatures.
1 Introduction
The arrival of quagga and zebra mussels to the Great Lakes Re-
gion in the 1980s caught many water treatment utilities off
guard by their biofouling potential.
1
Their ability to rapidly pro-
liferate, endure and disperse has allowed them to expand their
range over much of North America.
2
The mussels attach to sub-
merged infrastructure which clogs intakes, overwhelms equip-
ment and damages sensitive filtration membranes.
3–5
To com-
bat this threat, effective control methods are required that are
amenable to plant requirements and water conditions.
Within Canada, drinking water treatment facilities are lim-
ited to pre-chlorination as their sole method for controlling
quagga and zebra mussels. All methods of control are strictly
regulated by Health Canada and to date, only chlorine has
been approved for potable water use.
6
Fortunately, under ideal
conditions chlorine has proven to be effective at limiting mus-
sel biofouling and provides a balance of economics and chemi-
cal familiarity.
7,8
Chlorine is not without its disadvantages, as
it can react with organic precursors in raw water to form disin-
fection by-products (DPBs) of varying toxicity,
9
some of which
are regulated.
10
Certain utilities may require a pre-chlorination
substitute to meet both current and future DBP regulations,
while still providing adequate biofouling control.
11
Many alternatives to chlorine could be used to control
Dreissena. This includes most oxidants such as ozone, perox-
ides, potassium permanganate, ferrate and chlorine
dioxide.
12–16
Much like chlorine, these compounds create a
noxious environment that is detrimental to both Dreissenid
adults and their larval veligers. However, complete control re-
quires near-continuous exposure to oxidant residuals to in-
duce mortality, which may not be achievable for all treatment
scenarios.
15,17
Some water treatment plants operate on a cyclical produc-
tion schedule due to a combination of discounted nighttime
energy prices, oversized capacity, and flexible treatment pro-
cesses. This discontinuous flow regime may not allow for oxi-
dant residuals to be maintained during periods of stagnation.
Oxidant levels can subsequently decay below the mussel con-
trol thresholds.
18
This can allow for mussel fouling to occur
within the plant infrastructure, requiring manual removal.
19
A
more persistent chemical option would be advantageous to
provide adult control, while also being suitable for potable wa-
ter. Copper-based products have been found to meet these
criteria, as they are toxic to Dreissena and are often used for al-
gae control in potable water.
20
Current Canadian guidelines al-
low copper concentrations in drinking water of up to 1 mg L
−1
(an aesthetic limit), with a proposed new maximum acceptable
Environ. Sci.: Water Res. Technol.This journal is © The Royal Society of Chemistry 2019
Department of Civil Engineering, University of Toronto, 35 St. George Street,
Toronto, Ont, M5S 1A4, Canada. E-mail: ian.lake.thompson@mail.utoronto.ca
Water impact
Drinking water treatment plant intakes in North America are vulnerable to disruption by invasive quagga and zebra mussels. This research demonstrates
that a copper-based molluscicide may be effective at inducing adult mussel mortality under the conditions tested, and may offer an alternative to the more
traditional chlorination under circumstances where chlorine is not practical or effective.
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concentration (MAC) of 2.0 mg L
−1
deemed protective of both
short and long-term health effects.
16,21,22
The California 2008
public health goal for copper in drinking water is 0.3 mg L
−1
.
23
Copper concentrations required for mussel control are likely to
be significantly below these limits, suggesting that it might be
a viable treatment alternative. Nevertheless, the authors ac-
knowledge that the application of copper as a treatment chemi-
cal warrants careful consideration. The purpose of this study is
not to endorse the use of copper as a molluscicide, but to re-
port on its technical capabilities.
Prior studies into the behavioral effects of copper on
Dreissena polymorpha found that copper concentrations of 41
μgL
−1
resulted in a 50% reduction in filtration, with a com-
plete reduction at 100 μgL
−1
. Mussels were also found to ac-
cumulate copper once concentrations reached 28 μgL
−1
,
which may indicate the lowest feasible dosing threshold for
control of adults.
24
Sustained exposures of copper eventually
disrupts the mussel's normal physiology inducing mortality
via a range of mechanisms.
25,26
Copper speciation must also
be considered, as Dreissena have been found to thrive in wa-
ters with background copper levels as high as 62 μgL
−1
un-
der certain conditions of elevated pH, hardness and presence
of organics. It appears that the bioavailability of the copper is
affected by interactions with carbonates, hydroxides and the
formation of ligands with natural organic matter.
27
A number of copper-based products originally developed
as algaecides have been repurposed for mussel control, as
they often contain formulations to aid in dispersing copper
once applied to surface waters. One potential control option
is EarthTec QZ, which uses a proprietary formulation that is
claimed to maintain copper in solution and to increase its
bioavailability.
28,29
The California Department of Water Re-
sources trialed of a number of copper based products and
found that EarthTec QZ provided better control of both
Dreissena species within the trial timeframe.
30
The product's
formulation is reported to allow stable copper residuals to be
achieved, and unlike chlorine, without the formation of chlo-
rinated DBPs.
Previous investigations concerning the efficacy of this cop-
per product for adult mussels focused upon short-term expo-
sures, with a greater focus on copper doses above 300 μg
L
−1
.
28,30
This has left a data gap regarding doses that would
be more economically feasible for a water utility. Prior testing
has also been undertaken with water quality and test condi-
tions that are not representative of the Great Lakes Region.
The objective of this study was to investigate EarthTec QZ
as a potential control alternative for Dreissena. The study was
aimed at reactive control for managing established adult
mussels, as they present the most challenging life stage to
eradicate. Future work will examine the ability of this product
to prevent the settlement of mussels in their veliger stage.
2 Experimental design
The experiment was conducted over 4 months. The goal was to
gauge the effectiveness of a select number of copper doses to
control healthy adult mussels, under both continuous and dis-
continuous flow conditions. Chlorine was used to provide an ox-
idant treatment comparison. The experimental conditions are
summarized in Table 1, with each condition tested in triplicate.
2.1 Permitting
Products used to control zebra and quagga mussels are con-
sidered pesticides under Health Canada's Pesticide Manage-
ment Regulatory Agency (PMRA). EarthTec QZ is EPA and
NSF 60 certified for potable water systems in the USA and is
presently undergoing PMRA registration in Canada. A Re-
search Authorization permit was needed to perform testing
outside of the laboratory. Final PMRA approval granted the
Research Authorization number 0070-RA-17 under which the
study was performed.
3 Materials and methods
3.1 Test location and water source
To guarantee a continuous supply of raw water and to mimic
realistic environmental conditions, an in situ pilot approach
was used, located at the R.C. Harris Water Treatment Plant
in Toronto, Canada. The system draws water from Lake On-
tario using intakes located approximately 1300 meters from
shore in 15 meters of water. Sample lines on the exterior of
the intakes supplied the unchlorinated raw water.
3.2 Pilot system
A custom-made pilot system was used to continuously apply
the treatment chemicals to the experimental units, with the
system designed in-house but constructed by Morrflo of Bur-
lington, Canada. The pilot system allowed 12 parallel water
streams to be dosed simultaneously (Fig. 1).
3.3 Biobox setup
Bioboxes were used as flow-through aquaria to house the
adult mussels for testing (Fig. 2). The bioboxes provide an en-
vironment conducive to mussels and simulate the flow condi-
tions found in water treatment intakes. Each biobox was
plumbed into a corresponding trial stream from the pilot
unit, with the biobox outflow directed to a sanitary drain. All
Table 1 Experimental conditions tested
Product
tested
Concentration as Cu (μgL
−1
)
or total Cl
2
(mg L
−1
)
Flow
condition
Controls 1 and 2 —Continuous
Earthtec QZ 30 Continuous
Earthtec QZ 60 Continuous
Earthtec QZ 90 Continuous
Earthtec QZ 120 Continuous
Earthtec QZ 120 Discontinuous
Earthtec QZ 180 Continuous
Earthtec QZ 360 Continuous
Earthtec QZ 500 Continuous
Chlorine 1.0 Continuous
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units were covered with tarps to mimic the preferred dark en-
vironment of Dreissena.
31
A group of bioboxes was also modi-
fied to mimic the conditions experienced by discontinuously
operated plants by elevating three existing bioboxes with the
outflow from each unit directed to three different bioboxes
located underneath. A timer-activated valve with a piped over-
flow was then used to either direct or bypass flow to these
units on a 12 hours on/12 hours off cycle. Two biobox units
were also used as acclimatization boxes to allow adult mus-
sels to adjust to water conditions and to sustain them be-
tween experiments. These units were supplied with untreated
raw water from the control units.
Bioassay trays (Fig. 3) were constructed to securely house
the adult mussels used in the test. Trays were selected over
the typical bagging method, as they allowed easy observation
of the mussels with minimal disturbance.
32
The bioassay
trays were fabricated by modifying plastic baskets with #7
PVC mesh.
3.4 Reagents
The following analytical reagents were obtained for sample
preparation and the creation of standards for ICP-AES analy-
sis. This included trace metal grade nitric acid and an ICP-
Fig. 1 Pilot dosing system.
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AES grade copper standard, which were purchased from
VWR, Canada. Milli-Q®ASTM Grade I water was used for
stock solution preparation. When possible, all solutions were
prepared gravimetrically to limit cross-contamination.
Due to its registration as a pesticide, special permitting
was required to import the copper product from the manu-
facturer in the United States (Earth Science Laboratories,
Bentonville, Arkansas). All stated concentrations of the cop-
per product are with respect to copper content, with the pri-
mary stock having a copper concentration of 59 400 mg L
−1
.
To achieve the desired copper concentrations in the stock so-
lutions, the product was diluted with Milli-Q®ASTM Grade I
water.
Stock solutions of free chlorine were prepared from so-
dium hypochlorite (NaOCl) (10–15%) reagent grade (VWR,
Canada) and were diluted with Elix®ASTM Grade II water.
Dilutions were done to obtain the required applied dose to
achieve the target residual.
To achieve the different chemical doses for the various tri-
als, each of the 12 dosing pump channels had a dedicated
chemical storage container with differing stock concentra-
tions. The concentration of the copper solutions was in direct
proportion to the desired dose for the trial, as the copper
concentrations did not significantly diminish once dosed to
the bioboxes. To achieve the required total chlorine residual
leaving the biobox, in situ testing took place to determine the
required applied dose, as this methodology helped to better
incorporate the chlorine demand over the dosing timeframe.
Chemicals were dosed for 1 day prior to starting the experi-
ments to ensure stable residuals were achieved and stock so-
lutions were prepared as required throughout the
experiment.
3.5 Adult bioassays
All adult mussels used for this study were collected from a
marina on Lake Ontario (44°00′04.6″N76°59′27.9″W). Clusters
of adult mussels were carefully removed from the lake sub-
strate to minimize damage to the mussels. The mussels were
stored in coolers filled with lake water and transported to the
R.C Harris plant where they were placed in acclimation boxes
within 3 hours of being harvested. The mussels were then left
in the acclimatization boxes for 2 weeks prior to starting the
experiments.
100 adult mussels were taken from the acclimatization
boxes and placed into the bioassay trays. Care was taken to
leave mussels in their natural clusters to minimize stress and
to limit damage to their byssal threads. The bioassay trays
were then placed back into the acclimatization boxes for 24
hours prior to transferring them to the experimental bio-
boxes. Mussels were reexamined during this final transfer to
recount the number of mussels and to remove any deceased
individuals. If required, individuals were added or removed
to maintain a total count of 100. Over 3300 adult mussels
were used over the various trials with the majority being
quagga mussels, with the occasional zebra mussel noted
(≪1%).
3.6 Analytical methods
Chemical residuals were confirmed using a number of
methods, with extended chemical drawdowns providing sim-
ple validation of applied doses. The volume in each chemical
storage container was measured daily and the elapsed time
between measurements and stock concentration was then
used to calculate the applied dose.
Field measurement of copper was performed using por-
phyrin (Hach Method 8143) or bicinchoninate (APHA Method
3500) (HACH Method 8026) colorimetric methods, using ei-
ther a HACH 1800 or 5000 spectrophotometer. Reagent
blanks were composed of raw water prior to entering the pilot
system and unless otherwise noted all copper concentrations
are referenced to applied dose. The porphyrin method is not
APHA or USEPA approved due to the potential for
unexplained interferences in the water matrix, which necessi-
tates secondary confirmation.
33,34
To further confirm the cop-
per dose, ICP-AES analysis was performed using a Perkin
Elmer-7300 in accordance with USEPA Method 200.7 (ref. 35)
Fig. 2 Bioboxes used to house adult mussel bioassays.
Fig. 3 Bioassay trays used to contain adult mussels for testing.
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and 3125 B.
36
These were performed using representative
grab samples throughout the experiment and the method de-
tection limit was 1.34 μgL
−1
. ICP-AES confirmed that colori-
metric techniques provided an accurate measurement within
the raw water matrix with variations of less than 10%; how-
ever, occasional confirmation via ICP-AES was still performed
due to the potential for variances in background water chem-
istry. All sampling containers and glassware adhered to EPA
requirements for trace metals analysis. This included either
obtaining new certified “metal free”containers or extended
acid washes between glassware uses.
35
The concentration of free and total chlorine residual was
determined using DPD colourimetry Method 2350,
36
using
HACH 8021 and 8167 methods respectively. A HACH 1800 or
5000 spectrophotometer was used to perform the
measurements.
Mortality of each test group was checked every 24 hours
from the beginning of the trial until all individuals had
perished. To determine the vital status of the mussels, they
were examined for obvious signs such as gaping, their re-
sponse to physical stimulation, and behavior. Mussels were
categorized as follows based upon prior adult mortality
studies:
14,37–39
•Dead (when shell positon was gaping, no response to
physical stimulation and shell unable to remain closed when
depressed).
•Alive.
•Healthy (initially open, respiring, siphon visible and
rapid closure when stimulated).
•Stressed (initially open with slow response to
stimulation).
•Closed (shell closed with no response to stimulation).
A conservative approach was taken for undetermined indi-
viduals and they were left for the following day's assessment.
Mussels that were considered dead were removed from the
trays and recorded on a log sheet. These dead individuals
were then placed into a secondary storage container for the
duration of the experiment, to confirm counts. Closure re-
sponse, clumping and byssal thread condition were also ob-
served within the test groups as this can provide qualitative
information regarding mussel behaviors when exposed to
control products.
3,40
4 Results
4.1 Background water conditions
Water conditions during the course of the experiment
remained relatively stable, with many parameters (e.g. tem-
perature, hardness, pH, calcium) within prescribed ranges
for good to excellent growth for Dreissena species
17
(Table 2).
Water chemistry can also impact the efficacy of control prod-
ucts either through the interference of active ingredients or
disruption of normal mussel activity.
41
It may be of value for
future studies to compare the effect of pH, natural organic
matter, calcium, and hardness on the bioavailability of the
EarthTec QZ in differing source waters.
32,42
4.2 Adult mussel characteristics
Mussel age and size can influence the efficacy of a control
product, with previous studies noting increased resistance to
copper at later life stages compared to veligers or juvenile
adults.
16
Characterization results of test organisms are shown
in Fig. 4, and indicate that the majority would be considered
mature.
44
Typically, mussels that may have colonized water
treatment facilities would not reach this stage of growth if pro-
active management is taking place and mussels of this maturity
would represent a worst case scenario.
45
Mussel susceptibility
to molluscicides can vary throughout the year, possibly tied to
cumulative expenditure of energy reserves for reproduction.
46
4.3 Trial results
Temperatures within the bioboxes varied between 10.9 °Cand
5.2 °C over the course of the experiments, reflective of realistic
Lake Ontario conditions. This temperature range is also near
the lowest temperature threshold where chemical control
would typically be used and provides a more robust tempera-
ture challenge, as copper toxicity on mussels typically decreases
with water temperature.
26
Dissolved oxygen levels were within
an ideal range of between 8.6 mg L
−1
and 9.8 mg L
−1
,with
higher concentrations found in the cyclically-operated bioboxes
after 12 hours of stagnation.
47
Although the copper product is
acidic in nature, the low volumes of product used combined
with the buffering capacity of the water negated any discernible
pH depression between test groups.
Control groups used during this study exhibited less than
2% mortality during the period of the treatment experiments.
This indicates that test organisms were healthy and that experi-
mental conditions were conducive to survival. Mussels were ob-
served filtering and smaller groupings of mussels amalgamated
into larger clusters. Byssal threads were also produced to ad-
here to the bioassay trays. The extended acclimatization period
Table 2 Background water chemistry (from 4 samples)
Parameter Unit Average
Standard
deviation
Alkalinity mg L
−1
as CaCO
3
95.25 1.50
Calcium mg L
−1
36.63 0.83
Conductivity μScm
−1
302.75 4.87
Dissolved solids mg L
−1
195.00 5.00
pH mg L
−1
8.09 0.07
Hardness mg L
−1
129.00 3.16
Magnesium mg L
−1
9.12 0.32
Chloride mg L
−1
23.10 0.16
Potassium mg L
−1
1.58 0.04
Sodium mg L
−1
13.80 0.46
Sulphate mg L
−1
23.55 0.25
Copper μgL
−1
17.10 1.76
Nitrate (as N) mg L
−1
0.35 0.06
DOC mg L
−1
1.88 0.08
Chlorophyll a
a
μgL
−1
1.5 —
Total phosphorus
a
μgL
−1
8—
Turbidity NTU 0.16 0.16
a
Ref. 43.
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before performing the experiments appeared to be beneficial to
exclude poorly conditioned individuals.
From a qualitative perspective, the application of mollusci-
cides to the test groups resulted in varying levels of response.
Copper doses of 30 μgL
−1
and 60 μgL
−1
did not induce an
immediate acute behavioural response. Mussels continued to
filter and conglomerate into clusters, though some mortality
was observed. Once 40–60% mortality was achieved, mussel
behaviour began to shift, with decreased filtration and byssal
thread detachment occurring within some of the clustered in-
dividuals. Higher doses of copper caused siphon withdrawal
and byssal thread detachment within a few days of starting
treatment, illustrating that exposure and detection thresholds
may exist. Prior studies have found that copper levels above
100 μgL
−1
can quickly hinder respiration in zebra mussels,
leading to a range of cascading effects on their biology.
26
Chlorinated groups ceased to filter within the first day and
did not attempt to conglomerate during the experiment.
Cluster detachment also occurred within the first few days of
treatment. This is a typical response by mussels when faced
with an irritant or noxious compound.
48
All tested copper doses were found to provide complete con-
trol of adults, though the required dosing time frames changed
relative to applied doses (Fig. 5). Higher concentrations of cop-
per coupled with time of exposure led to higher levels of mor-
tality (ANCOVA, p<0.0001). The 1.5 °C variation in
Fig. 4 Mussel physical parameters based upon a random subsample of trial subjects. Mass is wet mass including the shell.
Fig. 5 Compiled dose response curves. Each data point is the average of triplicate trials.
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temperature between groups over the course of the monitoring
was not a significant factor (ANCOVA, p>0.05), though the
majority of experiments were completed within a similar tem-
perature range (9.0 ± 1.4 °C). All test groups exhibited a similar
dose–response relationship, with cumulative mortalities follow-
ing a sigmoid dosage-mortality curve.
25
The lowest applied cop-
per dose of 30 μgL
−1
required 28 days to reach 100% mortality,
whereas the highest dose of 500 μgL
−1
required only 7 days.
Cumulative mortalities were consistent between replicates,
with the majority of the variability exhibited during the mid-
points of the trials.
Chlorination comparison trials required 41 days to achieve
complete control, with a lag period of 7 days prior to any
mortality being exhibited. The applied dose of sodium hypo-
chlorite was equivalent to 1.35 mg L
−1
, which typically pro-
duced a total chlorine residual of 1.0 mg L
−1
and a free chlo-
rine residual of 0.91 mg L
−1
leaving the bioboxes. Water
conditions were fairly constant, which resulted in minimal
changes in chlorine demand during the trial; however, the
dosing system was solely proportional and could not respond
to intermittent changes in demand. Total chlorine residuals
ranged between 0.93–1.12 mg L
−1
, with a trial average of 1.02
mg L
−1
, while free chlorine residuals ranged between 0.81–
0.96 mg L
−1
, with a trial average of 0.91 mg L
−1
. The average
temperature of the trial was 6.7 °C, which resulted in a mor-
tality timeframe that is consistent with ranges found in prior
studies.
15,49
4.4 Cyclical flow comparison
The copper product was found to provide similar levels of
control when water was flowing continuously through the
bioboxes, and when flow was provided in a 12 hour on/off cy-
cle to represent intermittently operated treatment plants.
Both trials were dosed with 120 μgL
−1
as copper, resulting in
100% mortality after 13 and 12 days respectively, as shown in
Fig. 6. Copper residuals measured in the cyclical flow groups
after 12 hours of stagnation did not vary significantly from
the continuous groups, but water temperatures varied slightly
between the two trials, with a saw-toothed pattern emerging
from the extended stagnation periods and subsequent
warming in the cyclical groups. This resulted in average tem-
peratures of 8.5 °C and 7.8 °C in the cyclical and continuous
groups respectively, which may explain the slight differences
in mortality timeframes. This temperature pattern is repre-
sentative of some full-scale plants that operate cyclically with
the magnitude of warming dependent on ground conditions
surrounding the intake structure, with changes of 4–5°C
reported in one instance known to the authors.
50
The results
indicate that the product's effectiveness for adult control is
not significantly impacted by extended stagnation periods of
up to 12 hours, which are common in cyclically operated
plants.
5 Summary and discussion
All tested copper concentrations were found to induce mor-
tality in comparison to the control groups, with shorter cu-
mulative mortality intervals associated with higher copper
concentrations. This trend is illustrated in Fig. 7 and also
shows the lessening returns of greater copper doses. An area
of interest exists around the 120–180 μgL
−1
range, as this in-
flection appears to be a threshold where a point of
diminishing returns may exist. If examined from a concentra-
tion (C)×time (t) perspective this becomes very apparent
with a 4-fold time difference to 100% mortality between the
30 and 500 μgL
−1
doses (28 vs. 7 days), despite a 16-fold dif-
ference in concentration. Due to the realistic pilot conditions
and differing treatment intervals, small temperature varia-
tions existed between the different test groups; however, the
overall impact was not significant to the overall trend. Chlori-
nation required 41 days to provide complete control;
Fig. 6 Comparison of the copper product's (120 μgL
−1
) efficacy under differing flow regimes. Error bars represent the maximum/minimum of
triplicate trials.
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however, the abilities of oxidizing compounds to dissuade
the initial settlement must not be discounted, as total chlo-
rine residuals as low as 0.3 mg L
−1
can still provide an effec-
tive deterrent.
13,39
Pre-chlorination is the industry standard
for mussel control, so for a new alternative to be feasible it
needs to provide a comparable level of control.
The performance of the copper product indicates that it
has the potential to fulfill this requirement, as illustrated in
this study. Full scale adoption would require economics to be
considered, which necessitates consideration of a number of
factors. Applying real-world prices
51
to this study results in
the lowest copper dose being approximately 1.5 times more
costly per unit of water treated compared to the applied dose
of sodium hypochlorite, which is similar in scale to other
control alteratives.
8
Another factor is the disparity between
the required volumetric doses of the two undiluted products,
with the copper product requiring 22-times less volume per
unit of water treated. This could be advantageous with re-
spect to storage and dosing system requirements.
Copper doses below 120–180 μgL
−1
could be suitable for
continuous application, for facilities that require ongoing
control of adults. Although not included in this study, there
is the possibility that these doses may not proactively prevent
settlement; however, the threshold for veliger sensitively will
be lower and any settled individuals would eventually be
killed prior to reaching any significant size. This may be of
value when considering this copper product for proactive
control to deter initial settlement.
25
The lack of behavioral
changes in the test subjects were apparent in copper concen-
trations below 120 μgL
−1
and elevated doses were required to
illicit an obvious response; however, colder temperatures may
have depressed mussel activity. For facilities that cannot tol-
erate any degree of fouling this may be important and re-
quires further investigation.
Dosages above 120–180 μgL
−1
could be used for short
term discontinuous applications to kill any established mus-
sels, which could either be done at fixed intervals throughout
the typical mussel treatment season or as an end of season
treatment. This could complement existing control programs,
which either have poor adult control or have lower mussel
fouling levels. The ability of the copper product to maintain a
stable residual may provide a valuable mussel control option
for water treatment systems which operate cyclically. This is
presently an issue with facilities that rely on oxidants, as ex-
tended stagnation periods can lead to residuals decaying be-
low control thresholds.
6 Conclusion
A copper based molluscicide was evaluated at the pilot scale
to determine its efficacy for the control of adult Dreissena
mussels. The study was performed to gauge the molluscicide
Fig. 7 Summarized trial trends for EarthTec QZ and chlorinated comparisons. Error bars represent ranges of observations in triplicate trials.
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applicability for water treatment plants in the Great Lakes Re-
gion, as well as to investigate its potential to address the defi-
ciencies provided by current control methods. The study in-
cluded a range of copper doses, differing flow regimes and a
chlorinated comparison.
For the experimental conditions tested it appears that the
copper based product can be considered a feasible control op-
tion for adult quagga mussels in drinking water plant intakes.
Copperdosesaslowas30–60 μgL
−1
required a shorter
timeframe to provide complete control of adults compared to a
1mgL
−1
total chlorine residual (0.91 mg L
−1
free chlorine). A re-
lationship was observed between copper doses and the required
exposure time, with diminishing returns beyond 120–180 μgL
−1
.
Importantly, the copper product appears to be effective in
both continuous and cyclical flow regimes, with the latter be-
ing susceptible to oxidant decay. This could provide a valu-
able alterative to oxidant based control methods. Oxidants
such as chlorine do have a deterrent effect on Dreissena set-
tlement and further investigations may be required to explore
if low doses of the copper product also share this ability.
The authors wish to reiterate that any plans to adopt cop-
per as a molluscicide should include consideration of not
only its inherent properties as a molluscicide, but also con-
sideration of its potential adverse health effects at high con-
centrations. Furthermore, the fate of copper through the
drinking water/wastewater cycle and subsequent emission
back into the environment should be considered.
Conflicts of interest
No funding was received from the product manufacturer for
this research.
Acknowledgements
The authors are grateful for the support provided by Renata
Claudi of RNT Consulting Inc. and Toronto Water. This work
was funded by the Natural Sciences and Engineering Research
Council of Canada Industrial Research Chair in Drinking Wa-
ter Research at the University of Toronto. No compensation
was received from the manufacturer of the copper product
tested in this work.
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