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tivariate Analysis of Correlations Between Environmenta
Parameters and Cadmium Concentrations in Hyalella azteca
(Crustacea: Amphipoda) from Centra Ontario Lakes M. Stephenson1
and C. L. Mackie
Department of Zoology, University of Cuelph, Guelph, Ont. N 9 C
2W1
Stephenson, M., and 6. L. Mackie. 1988. Multivariate analysis of
correlations between environmental parameters and cadmium
concentrations in Hyalella azteca (Crustacea: Amphipda) from
central Ontario Bakes. Can. j. Fish. Aquat. Sci. 45: 1705-1 75
0.
Cadmium concentrations in Hyalelda azteca collected from 69
central Ontario Bakes ranged from 8.1 3 to 56.6 kg/$ dry mass.
Principal components analysis followed by multiple linear
regression found three principal com- ponents, interpreted as water
hardness, total cadmium, and dissolved organic carbon
concentrations, to be sig- nificantly (p =S 0.002) correlated with
cadmium concentrations in H. azteca. Cadmium concentrations in H.
azteca were independent of cadmium concentrations in littoral
sediments. It i s suggested that cadmium ions compete with calcium
ions for uptake sites on the gill surfaces of H. azteca. High
concentrations of dissolved organic carbon may complex free cadmium
ions and reduce their concentration in solution, leading to lower
cadmium concentrations in H. azteca. Les teneldrs en cadmium chez
des specimens d'Hyalella azteca prelev6s dans 69 Bacs du centre de
ItOntario 6taient comprises entre 0,13 et 56,6 de masse sGche.
L'analyse des cornposantes principales suivie d'une regression
lineaire multiple a permis de dkceler une correlation significative
(p 0,002) entre trois grandes composantes (durete de I'eau, cadmium
total et concentration en carbone organique dissous) et les teneurs
en cadmium relevees chez H. azteca. Les teneurs en cadmium chez H.
azteca 6taient independantes de la teneur en cadmium des sgdiments
Iittoraux. Ces donnees semblent indiquer que les ions cadmium
rivalisent avec les ions calcium pour les sites de fixation la
surface des branchies chez H. azteca. Des teneurs elevees en
carbone organique dissous peuvent former des complexes avec des
ions cadmium libres et rau i re Jeur concentration dans la
solution, ce qui entraine des tenem en cadmium plus faibles chez
68. azteca. Received july 3, 1987 Accepted May 3 7 , 1988
(J9.344)
xcept for a local area of high Cd deposition mew SSaabury, h e
central Ontaris region has a generally low and uniform Cd
deposition rate (Chan et al. 1986). However, low pH
has been shown to elevate Cd concentrations in Scandinavian ( H
e d s e n and Wright 1978; Borg 1983) and Ontaris (Ste- phenson and
Mackie 1988) lakes. Consquently, Cd concen- trations in central
Ontario sudace waters range from iaradetect- able (
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FIG. 1 . Central Ontario showing the locations of the study
lakes. The square in the inset map sf Canada shows the approximate
location of the study m a .
overnight. Empty vials to be used for analytical reagent blanks
were dried simultaneously. After drying, the mimds were indi-
vidudly weighed ( & 5 pg) on a C& m d e l G2
eIectrobalmce.
Animals were wet-ashed in microcentrifuge tubes by adding 25 pH,
of reagent-grade (70%) HNO,, followed after 1 wk by 18 pL of 50%
H202. The digestate was subsequently diluted with 1.0 IIL of
distilled-deionized water, giving a sample matrix of 1 -7% HNO,.
Reagent blanks and reference materials were digested
simultaneously. Digestate solutions were ma- lysed by tungsten
furnace atomic absorption spectrophotometry (Scintrex AAZ-2 with
'Zeemm background correction). The technique was tested by
digesting and analyzing Cd concentra- tions in an NBS standard
reference mderkd (1566 oyster tis- sue). Measured Cd concentrations
(3.66 9 0.42 QSD) pg/g dry mass) agreed with the certified value
(3.5 pg/g dry mass.
Water samples were collected for routine chemical analysis
(Ca2+, Mg2+, Na+ , K + , Cl - , SO,'-, total Fe, total Mn, total P,
dissolved organic carbon (DOC)) by the Ontario Ministry of the
Environment, using techniques described in Ontario Min- istry of
the Environment (198 1). Lake vaea, perimeter, md mean and maximum
depth were obtained (where possible) from the Ontario Ministry of
Natural Resources (Fisheries Branch, Envi- ronmentd a%ynmics
Section),
The data were reduced by PCA. The raw data (with the exception
of pH) were nnn-normal, so Iogarithmic trmsfor- mations were
applied. Box plots (Tukey 1977) indicated that the transformed data
were approximately normally distributed. PCA's based upon the
correlation matrices, and using vxirnax rotations, were p r fomed
on the nomdized data. Stepwise (p 90.05) multiple linear regression
was used with mean Cd concentrations in H . azteca for each I&e
as the dependent var- iable, and PCB scores fm each lake on each
principal wm- ponent as independent variables, to identify
environmental vva- iables correlated with Cd concentrations in H.
azfeca.
Variables were removed from the data matrix if (1) they loaded
most strongly onto a rotated principal component which was
subsequently shown by linear regression to be mcomelated ggP >
0005) with cadmium concentratisns in H . azteca md (2 ) the
mean-square error of the multiple regression run with prin- cipal
components derived from the reduced data matrix was not
significantly different from the mem-squm error derived from the
original data matrix. The latter was tested using the F-amam
statistic (David 1952). In this way the original data matrix of 20
variables was reduced to 6 variables loading ow thee orthog- onal
principal components, each of which was significantly ('p d 0.002)
correlated with Cd concentrations in H. azteea.
Cadmium concentrations in H. azteea from central Ontario lakes
ranged from 0.13 to 56.6 pg/g (Table 1). Water m d sed- iment c h e
~ s t r y and lake morphometric data were available for 51 lakes in
which H. azteea was found. The 28 variables orig- inally included
in the PCA matrix and their means md ranges are given in Table 2.
These variables were reduced to six (Ca2+, acid-neutralizing
capacity (ANC), pH, Mg2+ , DOC, total Cd), loading on thee
principal components, without any significant (HP < 0.05)
increase in the mean-square e m r of the regression analysis of
variance. The loadings of variables on the thee prim cipd
components are given in Table 3. These thee principal components
account for 94% of the overall variance of the six- variable data
set and a e interpreted as follows: PC1 = Water hardness (Ca2+,
Mg2+, ANC, pH); P I 2 = DOC; PC3 = total Cd in water. The
regression of Cd in H . azteea versus the K A scores for each lake
on each principal component is s u m a - rized in Table 4. Each
principal component is significantly cor- related with Cd
concentrations in H. wzteca, and none of the retained variables can
be rejected.
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TABLE 1. Cd concentrations in Pi. aztem collected from lakes in
centrd Ontario. Unless otherwise noted in parentheses, the number
given is the mean of 18 detemimtions. NP indicates that H. azteca
was not found at the time of sampling.
Cd in Pi. azteca Lake Township (pg eQ/g d v mass)
Richard McFarlane Raft h h i Clearwater S i m n McCharles Attlee
Gainey Broker Tyson Mahzenazing Kakakiwaganda H m
Sollmm Cecebe Ahmic Old Man's Bell's (Silver) Spence Horn Bear
Rdney Bray King Eagle Deer Lk. M. Islands Vhalley cm* McCoy Hay
McKenzie Lit. Boulter Lk. St. Peter Whitefish Rock Louisa H w Cache
Source .Toe Potter Brule
C ~ P Lucky Ohlmmn Reid Big Bhlmann Ban's Fortune tong Schooner
Kitchen Mackie Shaw Bmle ends tone Will's Buckshot
Dill BroderIDill DillIBroder Broder Broder Graham Grahm Attlee
Attlw Attlee SalelAttlee Humboldt Servos Bigwssd Chapman Chapman
Chapmadcroft S pence Spence Spence Monteith Montieth Ryerson Machar
Machar Machar Lount h u n t ChapHnan/Croft k c k Sabine Sabine
SabineILyell McClure McClure Sprsule Nightingale Lawrence Lawrence
Canisbay Peck Pw WHunter Hunter Hunter
Miller Miller Miller Miller Miller Miller Miller Miller Miller
Miller Miller Miller Miller CBarendon Miller
TABLE 1. (Csnckerded) Cd in Pi. azteca
Lake Township ( ~ g Cd/g dry mass) Echo Ril Chub Little Wren
Beech Maple Green Pine Cranberry Hv Lake of Bays Heeney Dickie
Plastic Blue Chalk Red Chalk
M c k a n Ridout Ridout S herbome Stanhope Stmhope Guilfo1.8
Guilford Guilfsrd Cbffe y Franklin M c k m McLaan S herbome Ridout
Ridout
The adequacy of the interpretations of the principal comp- nents
was tested by multiple linear regression using the v k - ables
loading on the principal components as independent vm- iables
against Cd concentrations in H. cmztecce. Four sets of independent
variables were tested (Ca2 + , Cd, DOC; ANC, Cd, DOC; pH, Cd, DOC;
Mg2+, Cd, DOC). The model including Ca2-, Cd, and DOC has the best
fit as measured by the a-square, and the regression is summapized
in 'Table 5.
Cadmium concentrations in freshwater crustaceans are typ- ically
less than 1.0 pg/g dry mass (Zauke I982b; Jop and Wojtan 1982;
Pfosi 1983). Concentrations in excess of 2 pg/g are generally
associated with industrial contamination (Ander- son et al. 1978;
Kneip and Hazen 1979; Zauke 1981; Jop and Wo~tan 1982; Ddlinger and
Kautzky 1985 j. Excluding the value of 56.5 pg/g dry mass obtained
for a single specimen from Plastic Lake, Cd concentrations in H .
ceztecce from central Ontario lakes ranged from 0.13 to 3'9.3 pg/g
dry mass. Both the highest (Heeney Lake) and the lowest (Ohlmmn
Lake) con- centrations were recorded in remote lakes without known
direct sources of contamination.
Multiple linear regression of Cd concentrations in H . azteca
with the orthogonal-derived vaiiables (principal components) showed
that at least Qkree components account for significant amounts of
variation. Two principd components (PC%, PC3) have unambiguous
interpretations (DOC and total Cd concen- trations, respectively).
However, PC 1 was strongly correlated with Ca2 + , Mg2+, pH, and
ANC. Its interpretation is ambig- uous and must focus on whether
hardness cations or ANC (HC0,-, C0,2-) modify the availability of
Cd to H . aztecce.
Interactions between water hardness and trace metal toxicity are
well documented. It is thought that the protection afforded by
hardness is due to competition between divalent base (Ca2+, Mg2+)
and trace metal cations for binding sites, thereby reduc- ing
uptake and toxicity, Cadmium toxicity to G w m m s pulex is reduced
by high Ca concentrations (Wright and hain 198 I), and the process
of Cd accumulation has been linked with Ca metabolism (Wright
198Q). At "low" Cd concentrations (56 - 560 pg/L), arn equimolm
relationship between @a and Cd uptake was implied by Wright (1980).
This conclusion is partly SUP- ported by data from the present
study. Although Cd concentra-
Cm. J. Fish. Aquat. Sci., 1101- 459 I988
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TABLE 2. Variables included in the full K A matrix, their
geometric means, and ranges. Variable Mean Rmge
ANC (mqlL) Total P (pglL) Ca b @ L ) Mg (mgW Na (mg/L) K (mg/L)
F oJ&L) C1 (mg/L) so4 (mdL) Total Fe (m@L) Total Mn (mg/L) DOC
(mg/L) PH Total Cd in sediment (mg/kg dry mass) Sediment loss on
ignition (5%) Total @d in water (ng/L) Maximum depth (m) Mean depth
(m) Lake area (ha) M e perimeter (b)
TABLE 3. Loadings of enviromental variables on principal comps-
Rents, and percentage of the overall variance accounted for by each
component, Loadings of absolute value greater than 0.50 are
underlined.
Variable PC 1 PC2 PC3 Ca 0.965 0.054 - 0.179 PH 0.902 -0.048 -
0.352 ANC 0.882 0.220 - 0.360 Mi3 0.874 8.122 -0.114 DOC - 0.087
-0.994 - 0.043 Total Cd -0.312 0.055 0.948
% of total variance 56.51 17.65 19.98
TABLE 5. Stepwise multiple linear regression of log-transformed
@d concentrations in H. azteca versus Ca, Cd, md DOC in water for 5
1 lakes in central Ontario.
Variable Coefficient SE t P Intercept 1.182 0.264 4.47 C0.001 Ca
- 1.154 0.148 -7.78
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Cd: Ca MOLAR RATIO IN LAKE WATE R FIG. 2. Cd concentrations in
H. aateca versus Cd:Ca molar ratios in 1&e water. The fitted
line is described by the equation Iog ( ~ g C&g dry mass) =
0.832 (Bog Cd:Ca molar ratio) + 0.602 (n = 51, r = 0.86, p <
0.081).
chelators, may increase or decrease the bioavailability or tox-
icity of Cd to invertebrates. The net effect of high DOC con-
centrations in central Ontario lakes is to decrease the availa-
bility of Cd to H . azteca, although PC2 (interpreted as DOC) is
much less important as a predictor of Cd concentrations in H.
azteca than PC1 (Ca2+, h4g2+, ANC, pH) and PC3 (total Cd).
Conclusion
Cadmium concentrations in 8%. azteca are correlated with water
chemistry md are independent of sediment Cd concen- trations and
basin monphometry. Thee chemical parameters (Ca2+, total Cd, DOC)
explain 8 B -3% of the total variation in Cd concentrations of H.
azteca. It is likely that Ca2+ and Cd compete for uptake, while DOC
may complex a portion of the total aqueous Cd, reducing the
available ionic Cd concentration.
This paper formed a part sf the Doctoral thesis of M.
Stephenson. The input and critical comments of my Supervisor and
Committee (DKs. G . E. Mackie, P. J. Billon, T. B. Nudds, L C.
Woff), N. B. Ym, md D. W. Schhdler are gratefully acknowledged. 8.
Twlarnd assisted with field smpIhg. P. J. Billon (Ontario Ministry
of the Envi- ronment) provided water chemistry analysis. 6. Gale
(Ontario Min- istry of Natural Resources) provided lake
mnsrphometric data. D. Strickland (OMNIP) granted permission to
sample lakes in Algonquin Park. Funding was provided by NSEWC grant
No. GO918, m quip- ment grant from Xerox Cmada, md by Xerox and
Ontario Graduate Scholarships.
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