The English- System: 11. Suppression of Mercury and Selenium Bioaccumulation by Suspended and Bottom Sediments

JOHNB%i'. M. RUDDAND MICHAELA. TURNER Freshwater Institute, Department c.f FisBzeries and Oceans, 581 Unbversi~g'Crescent, Wblznigeg, Mata. R3T 21V$

Rum, 9. W. AND M. A. TURNER.1983. The English-Wabigr~sn River system: II. Suppression of mercury and selenium bioaccumulation by suspended and bottom sediments. Can. 9. Fish. Aquat. Sci. 40: 2218-2227. Bioaccumulation of "3Wg and 75Seby several members of the food chain, including fish, was followed in large in situ enclosures in the presence and absence of organic-poor sediment. When the sediment was absent. 203Hgwas bioaccumulated 8- to 16-fold faster than when it was either suspended in the water or present on the bottom of the enclosures. Mercury- contaminated and uncontaminated sediments were equally effective at reducing the rate of radiolabeled mercury biasaccurnanlation, apparently by binding the mercury to fine particulates making it less available for methylation and/or bioaccumulation. Based on these results, a mercury ameliorating procedure involving senlicdpntinuous resuspension of organic-poor sediments with downstream deposition onto surface sediments is suggested. The presence of sediments, in the water or on the bottom of enclosures, also reduced radiolabeled selenium bisaccumulation. The degree of inhibition (2- to IO-fold) may have been related to the concentration of organic material in the predominantly inorganic sediments. Implications of this research with respect to mercury-selenium interactions in aquatic ecosystems are discussed.

RUDD, J. W. M., AND M. A. TURNER.1983. The English- Wabigoon River system: HI. Suppression of mercury and selenium bioaccurnulation by suspended and bottom sediments. Can. J. Fish. Aquat. Sci. 40: 2218-2227. Nous avons suivi Ia bioaccumulation de "('3Hget de '"e dans plusieurs membres de la chaine alimentaire, y compris les poiissons, places dans de grandes enceintes in situ, en presence et en l'absence de sediments pauvres en matiere organique. En I'absence de sedi- ments, 20%IHg,est bioaccumulC de 8 h 16 fois plus ragidement que quand il est soit suspendu dans I'eau ou prksent sur le fond des enccintes. Ees sediments contarnines par le mercure et non contarninks ssnt tout aussi efficaces B kduire le tau de bis~accumulationde mercure radinactif, apparemment par fixation du lnercure sur de fines particules. ce qul le rend anoins accessible a Ia mkthylation ou a la bioaccumulation, ou aux deux. En nous fondant sur ces rdsulkats, nous suggCrons une rnkthode d9amtlioratisndu mercure, impliquant une resuspen- sion semi-continue des skdiments pauvres en matikre organique, avcc dkposition en aval sur les sCdiments suprficiels. La presence de skdirnents dans l'eau ou sur le fond des enceintes rdduiit egalement Ia bioaccumulatioan de selenium radioactif. Il se put que le degre d'inhi- bition soit reliC a %aconcentration du rnatkriel organique dans les sediments en grande partie inorganiques. Nous analysons les implications de cette recherche sous 17angIedes interactic~ns mercure - sdlCnium dam les kcosystt3nes aquatiques .

Received May 11, 1982 Accepted August 24, 1983

SUSPENDEDsediments are thought to play an important role in and Mn) coatings on the surfaces of clay particles (Andersson the bioconcentration of toxic substances (Gibbs 1973; Hem 1978, cited in Awdersson 11979; Jsnasson 1970; Hem 1972; 1976; Karickhoff and Brown 1978; Popp and Laquer 1980; Jackson et al. 1978; Andersson 1979; Jackson 1979). Tessier et al. 1980). They have often been considered as Sediments might also serve a beneficial role by reducing vectors capable of moving pollutants from their sources to the bioavnilabiIity of pollutants such as Hg. In the Hg- distant locations where the toxic substances can be accumu- polluted English-Wabigoon River system (Armstrong and lated by aquatic biota. At neutral pH the sediment-borne pol- Hamilton 1973), the two most important sites of Hg methyl- lutants may be associated with particulate or dissolved organic ation and bioaccumuiatisn are the water column and surface materials, clay mineral, or organic and inorganic (usually Fe sediments (Rudd et al. 1983). If sediments were deliberately resuspended as a Hg ameliorating procedure, they might Printed in (.I693 1) reduce Mg anethylation and bioaccurnulaticsn while the sedi- Imprim6 au Canada (96931) 2218 RUDD AND TURNER: SUPPRESSION OF Hg BIOACCUMULATION BY SEDIMENTS

TABLEI. Chronology of 1979 enclosure additions.

Days after isotope addition Addition

- - Enclosures filled 3 kg NaCl per enclosure yielding final concentrations of 13 mg Na. L-' 18 kg sediment added to the sediment addition enclosure 5.7 mCi Z0%Ig(~03)2and 1.4 mCi ~;'Se0, to each enclosure on June 4, 1979 40 dace per enciosure at MW initial density of 40 kg. ha-' 12 kg sediment added to the sediment addition enclosure 18 caged crayfish to each enclosure 6 caged clams per enclosure 12 kg sediment added to the sediment addition enclosure Fourth sediment addition to examine short-term radioisotope speciation Termination of experiment

TABLE2. Wabigoon Lake sediments taken from the central basin of Wabigoon Lake. Surface organic floc was removed during sampling. All analyses are presented on a dry weight basis.

5% sand 9% silt 96 clay Carbon Nitrogen Phosphorus Carbonate Total Hg Sample < 50 ym 50-2 ym < 2 pm (%) (%) 6%) (%B (lagsg-') Wabigoon Lake (as 9% of inorganic fraction) 9 46 42 - - - - - Wabigoon Lake (as 5% of total sediment) 9 48 41 2.0 0.2 0.07 8.3 8.83 ments were suspended in the water column and after they were enclosure), while tho two other enclosures were maintained deposited onto the surface sediments. This possibility was as controls. examined during 1978 and 19'79 using ecosystem-level ex- periments in large enclosures located in Clay Lake (5O0O3'N, 93"30'W), which is the first major reservoir of the English- Wabigoon River system. The experiments were designed to On day Q of the experiments (July 15, 1978; June 4, test the effects of sediment suspension on bioaccumulation of 1979) each enclosure received approximately 5.7 mCi of Hg by fish and other members of the food chain. 203Hg(N03)2(1 Ci = 37 GBq, approximately 15 ng Hg L-' The effect of sediments on rates of Se bioaccumulation was added as carrier) and about 1.4 mCi of ~24?3eO,(New was also tested. This was done because trace Se addition to England Nuclear). A single addition of foodgrade NaCl was Hg-contaminated waterways was being considered as an made to each enclosure for checks of enclosure leakage. The ameliorating procedure (Rudd et a!. 1980~;Rudd et al. 1983; resulting Naf and @I- concentrations were approximately Turner and Rudd 1983). twice preaddition levels, as determined by atomic absorption spectrometry (Stainton et al. 1977). No leakage was detected during the course of either of the experiments. The control enclosures received no other chemical addi- Two separate experiments were conducted in large en- tions. The 1978 plastic bottom enclosure received sufficient cBosures during the summers of 1978 and 1979. The en- NaHzP04 and NaPJ03 to maintain primary productivity rates closures were 10 m in diameter and either 2 or 1.5 m deep at the level of the control. For the 1979 experiment, sediment with a volume of abut 100 m3. They were constructed of was obtained from the central basin of Wabigoon Lake, which cross-laminated polyethylene as described in Rudd et al. was upstream of Clay Lake and was not Hg contaminated. (1980b, 1980~)except that most of the enclosures had water- The surface layer (0.5 cm deep) of recently deposited organic tight polyethylene bottoms. They were situated in a sheltered material was removed. Sediment was added to this enclosure bay of Clay Lake, northwestern (Armstrong and on three occasions (Table I). The first addition was approxi- Hamilton 19'73). The plastic bottom encIosures were filled mately 18 kg (dry wt) of Wabigoon Lake sediment while the over a 3-d period with Clay Lake epilimnion water. Pumps second and third additions were about 12 kg each. On each were moved repeatedly from enclosure to enclosure to ensure occasion, wet sediment (59% water) was suspended through- that water and plankton in all the enclosures were similar. out the water column of the suspended sediment enclosure by The 1978 experiment had a control enclosure with a bottom dispersing it into the wake of an electric outboard motor. of natural Clay Lake sediments and a test enclosure with a Sediment addition continued until the Secchi depth (Welch water-tight plyethylene bottom, which prevented contact 1948) was 20 cm. Particle size analysis of the sediment was with lake sediments. The I979 experiment had thee en- done by the pipette method (McKeague 1978). This material closures with sealed plastic bottoms. Sediment was added was largely conaposed of silt and clay-sized particles and was to the water column of one enclosure (sediment addition of a low Hg concentration (Table 2). The sediment additions CAN. J. FISH. AQUAT. SCB., VOL. 40, 1983

TABLE3. Secchi depth, total suspended solids, and He, data at four sites on Clay Lake during the open water season (May-Nov.) sf 1978.

------Secchi depth Suspended solids Total Hg CH,Hg + Site (mgSL-') (ng.L-') (V3-L '1 - -

Inflow 0.5820.10, N = 24 I0.4k2.1, N = I2 35.3910.7. N = 48 0.048 (;1.69),' 18.' = 22 (0.54k0.87, N = 9)" (9.2k0.8, N = 51h Eastern basin 0.6320.14, N = 24 8.523.5, N = 12 30.5214.0, N = 46 Western basin I.24?0.42, N = 23 2.320.9, N = 12 19.62 9.9, N = 3%

Outflow I .39+0.42, N - 24 2.428.8, N = I2 17.9k 7.4, N = 50 0.10 (:1.62),' N = 22 (1.29f0.29, N = 9)" (2.4k0.9, N = 51h "Sampled weekly during Aug. 23-Oct. 18. 'Sampled biweekly during Aug. 30-Oct. 25. 'One standard deviation is obtained by multiplying or dividing the log-normal mean by the factor given in parentheses. did not detectably increase Hg concentrations in the water of 0.25, 0.75, and 1.25 m of depth were combined, dried at the enclosures. 60°C, and weighed before radioisotope analyses. Movement of 253~gand 75Seinto the periphyton commu- nity was followed by assaying the periphyton colonized on polyethylene strips hung from the lake surface to a depth of The Hg isotope was added as 2"3~g2'and Se was added as 1 rn in the enclosures. After assay of its radioisotope concen- 7?3e032- (Table 1). A comparative radiochemical approach tration, the priphyton was dried at 608C, scraped from the was used for this experiment, as opposed to a radiotracer polyethylene, and weighed. These strips were uncolonized approach. This was done by adding identical quantities of when they were suspended in the enclosures at the time of the radioisotopes to each enclosure. Bioaccumulation of the enclosure installation. AII radioisotope data were decay cor- radioisotopes could then be compared between control and rected to the day of radioisotope addition, day zero of the test enclosures. Further details of the radioisotope rationale experiment. are presented in Rudd et al. (1983). The radioisotope bioaccumulation data are presented as Water samples were analyzed for 2"3H~and "Se speciation ratios in which the lognormal means of the radioisotope con- as in Hesslein et al. (1988) and Rudd et al. (B980b). The centrations (cpm per gram wet weight) of the test samples particulate fraction was obtained by sequential filtration were divided by the means of the control concentrations. through GF/C-Whatman and 0.45-pm Millipore filters. The filtrate was then passed through an activated charcoal column to obtain the fraction associated with organic material. This was followed by passage through a mixed cation - anion ex- During 1979, weekly estimates of cloudless primary pro- change column (Dowex 1 X $, 108-208 mesh and 50W- 12, 100-208 mesh) to remove the ionic fraction of the radio- ductivity were made using the I4C incubator technique as isotopes. Finally, any remaining or unassociated 253~gwas described in Rudd and Turner (1983). precipitated as 'OPHgS after oxidation to 20'~g'', as described Total Hg and methyl mercury concentrations in water were in Rudd et al. (1980b). analyzed according to methods described in Fumtani and Bisaccumulation of radioisotopes was monitored in cray- Rudd (1980). Total suspended solids were estimated as de- fish (Orconectes virilis) and clams (Anodonta sp.) caged indi- scribed in Stainton et al. (1977) except that samples were vidually in epoxy-coated wire mesh cages and in free- filtered with 0.45-pm membrane filters instead of glass fiber swimming pearl dace (Sernotilus ppzargarita). The crayfish filters. Water samples were taken at 2-wk intervals md ana- were fed an excess of white sucker (Catas~omuscommersoni) lyzed for total dissolved phosphorus, particulate carbon and flesh, which had a low mercury concentration of 0.2 pg *g-'. phosphorus, and dissolved organic carbon, as described by Five or six clams, crayfish, and gear1 dace from each en- Stainton et al. (1977). closure were analyzed on-each sampling date. All samples for "%g and "Se analyses were contained in small petri dishes (50 mm in diameter and 9 mm in height) and assayed by gmma spectroscopy (Hesslein et al. 1988; Rudd et al. Finescale dace (Chrosomus rzesgaerus) and pearl dace 1980b). Sample means were calculated from the log trans- were held for up to 8 wk in I-m3 braided nylon cages sus- formed data, which had been decay corrected to day O of the pended above the sediments at both the outflow and inflow of experiment. Clay Lake. Four individuals of each species were sampled by Zooplankton samples (i.e. particulate material greater than dip net on each sampling occasion and were frozen until 73 pm) were collected using a plexiglass trap (Schindler analyzed for Hg concentration by the method sf Armstrong 1969). For each sampling day, the contents of traps from and Uthe (1971). RUDD AND TURNER: SUPPUESSlON OF Hg BIOACCUMULATION BY SEDIMENTS

0

DAYS AFTER ISOTOE ADDITION

FIG.2. Secchi depth readings in the controls (C and X) and the suspended sediment enclosure (P). Arrows on the horizontal axis indicate additions of sediment to the sediment addition enclosure.

Crayfish 7?3e biioaccumulatiion was also about 10 times higher in the plastic bottom enclosure (data not shown). In the ab- sence of sediments in the plastic bottom enclosure, there was no detectable loss of 7%e from the water during the experi- ment (Rudd et al. 1980b). The residence time of '%e in the DAYS OF EXPOSURE water column of the control enclosure was 56 d (Rudd et al. 1980~). PIG. 1. Inhibition by natural Bake sediments of pearl dace and 75Sebioaccumulation expressed as ratios in which "%g and "Se concentrations of fish in an enclosure with a plastic bottom are 1979 EXPERIMENT divided by corresponding concentrations in fish maintained in an enclosure with natural lake sediments (C). Secchi depth in both control enclosures increased from 0.8 to 1.5 m between day -9 (i,e. 9 d before radioisotope addi- Results tion) and day $ (Fig. 2), and then remained at about 1.5 m (1 *464 0.24, + SD, N = 26) for the remainder of the experi- ment. Secchi depth in the enclosure to which sediment was to be added tracked the controls until the first sediment addition Wave action on the walls of the enclosures continually on day -3, which reduced the Secchi depth to 0.2 m. Secchl resuspended bottom sediments in the control enclosure main- depth increased until day 8 when a second addition of sedi- taining the Secchi depth within a range of 0.7- 1.0 m. This ment returned the Secchi depth to 0.2 m. Another addition Secchi depth was close to the average Secchi depth of the was made on day 22 after the Secchi depth had increased to eastern basin of Clay Lake where the enclosures were located 0.9 m. The average Seccki depth in the sediment addition (Table 3). Within 2 wk, Secchi depth in the enclosure with a enclosure after the first clay addition was 0.52 m (k0.20, sealed plastic bottom was greater than the depth of the control N = 20). During the same time period, total suspended solids enclosure (2 m) and remained at greater than 2 m depth for the (TSS) in the control enclosures were 2.0 mgeL-' (k0.0, duration of the experiment (56 d). The water column resi- N = 4). Total suspended solids were measured twice in dence time of ''%Ig in the enclosure with a plastic bottom was the sediment addition enclosure when the Secchi depth twice as long as in the control enclosure (36 vs 18 d) (Rudd was 0.3 rn. On these occasions, TSS were 13 and 18 mg * E- ' , et al. 1980~). dry wt. Radiolabeled Hg was bioaceumulated by pearl dace 8- 16 Phytoplankton primary productivity was generally similar times faster in the plastic bottom enclosure than in the control in the control and the sediment addition enclosures throughout enclosure, which had natural sediments and more suspended the experiment. However, immediately after sediment addi- particulate material (Fig. 1). At the end of the experiment tions, the decreased Bight penetration reduced daily rates of "3~gconcentrations in crayfish were 15 times higher in the primary productivity in the sediment addition enclosure by plastic bottom enclosure than in the control enclosure (data about a factor of 2 relative to the controls (-30 vs 60 mg not shown, the percent coefficient of variation of each mean C * m-'. d- ' ) . This difference diminished with time because concentration king about 20%). water transparency increased steadily after each sediment Selenium-75 bisaccumulation was also reduced by the addition (Fig. 2). Such reductions in primary productivity presence of sediments. Concentrations in pearl dace were are expected to have, at most, a small negative effect on 2-9.5 times higher in the plastic bottom enclosure (Fig. I). rates of Wg bioaccumulation (Wudd and Turner 1983). This is 2222 CAN. J. FISH. AQWAT. SCI., VOL. 40, 1983

will be overestimated because their radioisotopic concentra- tions were determined using filtered water. Long-term partitioning sf "Se was not affected by in- creased suspended sediment concentrations (Table 4). As in other experiments (Rudd et al. 1980b9 1980~;Turner and Rudd 19831, "Se in both the sediment addition and control enclosures was primarily associated with the particulate frac- tion (-55%) at the beginning of the experiment. This de- clined rapidly during the I st wk sf the experiment so that after day 9 about 55% of the 75Se in all enclosures was associated with the organic fraction (activated charcoal). There may have been a short-term effect of sediment addition on the parti- tioning of '%e. Immediately after the fourth sediment addi- tion on the last day of the experiment, the percentage of 75Se in the organic fraction increased from 57 to 75%. This '%e was drawn entirely from the ionic fraction, which decreased from 32 to 14% of the total '%e concentration. Biomass (grams per square centimetre) of periphyton on the polyethylene strips peaked on day 22 in all of the enclosures and was four times higher in the sediment ddition enclosure than in the controls. On that day, '""Hg and '%e concen- trations per gram of periphyton were lower by 50 and 75%'c, respectively, in the suspended sediment enclosure than in the 0 control enclosures. 0 18 20 The movement of both Hg and Se into the zcmplankton, DAYS AFTER ISOTOPE ADDITION crayfish, and pearl dace was very similar in both control FIG. 3. Concentrations (clam) of '03Hg (solid lines) and '-'St2 (broken enclosures, usually varying by

TABLE4. Partitioning of "%g and "~ein water samples taken from the 1959 control and sedimeaat addition enclosures. Means (&sf)) are reported for five samples taken at weekly intervals.

- -- - 5% particulate 96 charcoal Enclosure p0.45 pm) (organic) R ionic % unassociated

Control I 25.4 (28.1) Control 2 26.5 (24.9) Sediment addition 43.2 (27.8)

Control I 23.2 (k 14.9) Control 2 23.9 (? 19.0) Sediment addition 23.8 (216.9)

Keeney 1974; Olson and Cooper 1974: Armstrong and Scott residence time of the labeled Hg (Fig. 3), although Hg bio- 1979; Huckabee et al. 1979; Fumtani and Wudd 1980; Rudd accumulation was drastically reduced. This suggests that the et al. 1980a; Topping and Davies 1981). In the English- '"%Q in the suspended sediment enclosure was quickly bound Wabigoon River system the water column and the organic- either to dissolved organics added as part of the wet sediment rich surface layer of the sediments are thought to be the maJjor or to fine particulate material, which was permanently sus- contributors of methyl mercury to fish (Rudd et a]. 1983). The pended or sedimenting very slowly. Because there was no deeper organic-poor sediments, which underlie the surface detectable increase in dissolved or suspended organic carbon organic floc, and which may contain high concentrations of concentration in the suspended sediment enclosure as corn- Hg, are apparently not contributing substantially to the pared with the controls (data not shown), and because the present methyl mercury levels in the biota (Wudd et al. 1983). amount sf 203~gassociated with the dissolved organic frac- Our enclosure experiments were designed to establish if the tion was lower in the sediment addition enclosure (Table 4), presence of organic-poor sediment in either the water column it is likely that the labeled Hg was bound by the clay mineral or on the bottom of the enclosures could reduce the bio- fraction of the suspended sediments. Mercury is known to accumulation of methyl mercury. In the 1978 experiment, the bind to clay particles both by ion-exchange reactions and by organic-poor sediment was primarily on the bottom of the coprecipitation with organics or inorganics (Fe, Mn) onto the contrc~lenclosure with natural sediments - beneath the surfaces of clay-sized particles (Sonasson 19468; Lockwood organic-rich surface sediment. This location of the organic- and Chen 1974), and in hct, an increase in percentage of Hg poor sediment was probably the cause of a twofold reduction on particulate material was observed in the sediment addition in the residence time of 20%g in water as compared with the enclosure (Table 4). This observation was in agreement with plastic bottom enclosure. This may have been partially Amstrong and Hamilton (1973) who found that Hg was asso- responsible for the 10-fold reduction in Hg bioaccurnu8ation ciated primarily with the clay-sized fraction of Clay Lake by pearl dace and crayfish. Additionally. there was reduced sediments. In addition, Lindberg and Hmiss (1977) con- "%g bioavailabiiity in the water column of the control en- cluded that Fe and not organics was responsible for the closure with a natural sedilsaent bottom because of resus- scavenging of Hg after resuspension of sediments in labora- pension of organic-poor sediinent by wave action on the walls tory experiments. Also, Jackson et al. (1984) concliaded that of the enelosurcs. particulate-bound Hg was not readily available for bio- When organic-poor sediment from Wabigoon Lake accumulation. All of these observations indicate that in our (Table 2) was added directly to the water column in the 1979 enclosure experiments the binding of Hg to clay-sized par- experiment, there was no effect on residence time of 203~gin ticles, in both the water column and surface sediments, water (Fig. 3). Thus, in this experiment the large reduction reduced the bioavailability of Mg. observed in "%Ig accunzuiation by the biota (Fig. 4 and 5), This Hg binding process was probably operative in Clay including a reduction to 5% of the controls in pearl dace Lake, since suspended sediment concentrations in the lake muscle (Fig. 5). was likely a direct effect of suspended sedi- and in the 1979 enclosures were quite similareConcentrations ment. An overall interpretation of LBc~th experiments is that of suspended sediment, as measured by Secchi depth, aver- binding of '03& and/or CH3"'%-IHgby the organic-poor sedi- aged 0.5 m (?0.2? hi = 20) (Fig. 2) in the sediment addition ment, either in the water column or on the bottom, was an enclosure and 0.6 rn (Table 3) in the eastern basin of Clay effective inhibitor of Hg bioaccumulation. Lake. Suspended sediment concentrations in the western An examination of the relative rates of loss of suspended basin of Clay Lake, which had greater water clarity, were sediment and '"Hg from the water column of the I979 sedi- more closely approximated by the 1979 control enclosures. ment addition enclosure yielded information on the mech- The western basin Secchi depth averaged 1 .27 m (Table 3) as anism by which these organic-poor sediments reduced Hg compxed with 1.46 m (0.24, N = 26) (Fig. 2) in the control bioaccumulation. Sedimentation of the larger particulate ma- enclosures. terial resulted in increasing water clarity after each sediment To determine if the same type of binding mechanism addition (Fig. 2). However, this did not affect the water observed in the enclosures was operative in Clay Lake, an CAN. J. FISH. AQUAT. SCI., VOL. 40, 1983

A PEARL DACE WHOLE BODY

LL, 0 I3 PEARL DACE MUSCLE

0 0 18 20 DAYS OF EXPBSLBRE BAYS OF EXPOSURE FIG. 4~ Inhibition of 2"3Hg and 75Sebioaccumulation by zooplank- FIG. 5. Inhibition of '03Hg and "Se bioaccumulation in pearl dace ton and crayfish by addition of organic-poor sediment to an enclosure. whole body and muscle samples by addition of inorganic-rich sedi- The values presented are ratios in which m3Hg and 75Se concenrra- ment. Values presented are ratios in which '03Hg and 75Se concen- tions in biota of the sediment addition enclosure are divided by the trations in biota of the sediment addition enclosure are divided by the corresponding concentrations of the combined control enclosures (C). corresponding concentrations of the combined control enclosures (C).

TABLE5. Accumulation of ""Hg and "Se in the foot muscle of clams in the presence and absence of added sediment. The lognormal mean of 5 clams is reported for the sediment addition enclosure and of I0 clams for the combined controls. One standard deviation is obtained by amaultiplyirng or dividing the lognormal mean by the factor giveas in parentheses.

'03& '('7% '%%e 75~e Enclosure (cpm .g-I s~)(9 of controls) (spmeg-' SD) (% of ccmtrols)

Combined controls 265 ( 128) 100 190 ($1.48) 10Q Sediment addition 33 (s1.63) 13 143 (z1.73) 75 experiment examining Hg bioaccumulation by caged fish was dace accumulated mercury more slowly at the inflow than at carried out at the inflow and outflow sf the Iake where sus- the outflow where the suspended sediment concentrations pended sediment concentrations were quite similar to concen- were lower (Fig. 7; Table 3). This indicates that the Hg at the trations in the eastern and western basins (Table 3). During outflow was more available for methylation and bioaccumu- the 8-wk experiment suspended sediment concentrations and lation. The higher concentrations sf methyl mercury at the concentrations of total Hg, which was predominantly insr- outflow (Fig. 6) and the much higher ratio of methyl mercury ganic Hg, were higher at the inflow of the lake than at the to total Hg at the outflow (Table 3) also support this conelu- outflow (Fig. 6; Table 3). Even though the gig concentrations sion. The results of this experiment are in agreement with the at the inflow were higher, both the finescale dace and pearl observations of Parks et al. (1988) and Jackson and Woychsak RUDD AND TURNER: SUPPRESSBON OF Hg BBOACCUMULATION BY SEDMENTS

8 = INFLOW I~FLOW 0. OUTFMW P Pearl Dace F Finssccsk Docs

I I I I 0.10 ! r I I T 235 2W 265 280 295 235 250 26% 280 295 06T 22 WG 23 OCT 22 AUG 23 DAY OF I978 DAY OF 1978

Ro. 6. Concentrations of total Hg and methyl mercury at the FIG. 7. Total Hg concentrations in finescale and pearl dace caged inflow and outflow of Clay Lake during the late summer and fa!! at the inflow and outflow of Clay Lake during the late summer and of 1978. fall of 1978.

(1980) who found a progressive increase in the ratio of methyl bioaccumulation by pearl dace (Fig. 1) and crayfish (data not mercury to total Hg in the water of this river-lake system shown). At trace concentrations (c0.2 yg Se k '), Se is with increasing distance downstrearn from Dryden. As we known to be predominantly associated with organic material observed (Table 3), the increasing ratio of methyl mercury to (Table 2; Wudd et al. 198eBb, 1980~;Wudd and Turner 1983; total Hg also corresponded to decreasing downstream sus- Turner and Rudd 1983). During the 1978 experiment, pended sediment load. organic-rich material on the surface of the natural sediments may have bound the '%e reducing its bioavailability. This could have occurred on the bottom of the enclosure or after resuspension of the organic-rich n-aaterial by wave action on We were interested in the extent to which resuspension of the enclosure walls. During the 1979 experiment, predom- sediment would alter Se bioaccumulation because trace Se inantly organic-poor sediments were added to the sediment addition was being considered as a Hg ameliorating procedure addition enclosure. These observations suggest that presence (Wudd et al. 1983; Turner and Rudd 1983). This type of of organic-rich sediment may have a larger inhibitory effect information is also uscful in assessing the possible toxicity or on Se bioaccunnulation than organic-poor sediments. ameliorative effects of Se added to waterbodies from indus- The present Hg:Se atomic ratios of northern pike (ESO~X trial sources or by coal combustion (Klein et al. 1975). bucius) and walleye (Stizostedkora viereurn) in Clay Lake are Hn the 1979 experiment, addition of organic-poor sediment about 10: 1 (Rudd et al. l980b). Our observations that reduced the rate of Se bioaccumulation to 50-75% of the organic-poor sediment addition reduced anuscle Hg concen- controls in all members of the food web tested (Fig. 4 and 5; tration to 5% of the controls, and Se concentration to only Table 5). A similar effect was observed in a companion ex- 70%,, suggest that the Hg :Se ratio of fish in the English - periment in which an increased rate of primary productivity Wabigoon system could be reduced (improved) by addition decreased Se concentration in biota (Rudd and Turner 1983). sf organic-poor sediments to the water column and surface In that case, Se appeared to be diluted by the increased rate sediments of this Hg-polluted river system. of growth of the organisms. In the 1979 sediment addition experiment, the reduction was a direct effect of the organic- poor sediment, since growth rates of fish and phytoplankton were not significantly different from those in the controls. Ira the 1978 experiment, the presence of natural sediments Continuous or periodic resuspension of sediment by small was correlated with a much larger (10-fold) reduction in Se dredges followed by downstream deposition might be a 2226 CAN. J. FISH. AQUAT. SCH., VOL. 40, 1983 feasible arneliorartion procedure for the Hg-polluted English- the Freshwater Institute, the Canada Water Act. and the Government Wabigoon River system in which a large quantity of Mg of Ontario. is being continuously transported downstream (Rudd et al. 2983). Sediment resuspension followed by downstream depo- ANDERSSON,A. 1979. Mercury in soils. ln J. 0. Nriagu [ed.] The sition would attack the problem in both the water column and biogeochemistq of mercury in the environment. Elsevier/ the surface sediments - the two most iraaportant contributors North-Holland Biomedical Press, New York, NY. 696 p. sf Hg to &he biota (Rudd et al. 1983). In the water column and ARMSTRONG,F. A. J., AND A. L. HAMILTON.1973. Pathways of surface sediments, resuspended sediments would bind Hg rand mercury in a polluted lake. p. 131 -156. lrz P. C. Singer [ed.] Trace metals and metal-organic inter- reduce its bioavailability . Further, at the sediment surface, actions in natural waters. Ann Arbor Science Publishers Inc., increased deposition of clean, organic-poor material would Ann Arbor, MI. dilute concentrations of both Hg and organic carbon, the latter ARM~~ONG,F. A. J., AND D. P. SCOTT.1979. Decrease in mercury being a source of bacterial food. Both of these factors can content of fishes in Ball Lake, Ontario, since impc~sitionof control rates of microbial Hg methylation in Clay Lake sur- eontroIs of mercury discharges. J. Fish. Res. Board Can. 36: face sediments (Fumtani and Rudd 1980; Rudd et al. 1983). 670-672. In support of our ccsnclusions, Parks et al. (1984) found that ARMS~ONG,F. A. J., AND 3. F. UTHE.1971. Semi-automated deter- methyl mercury concentrations in fish are conelated with mination of mercury in animal tissue. At. Absorpt. News[. 10: local water and surface sediment Hg concentrations through- 101-103. FURUTANL,A., AND J. W. M. RUDD.1980. Measurement of mercury out the river system. methylation in lake water and sediment samples. Appl. Environ. The approach described above might prove useful for other Microbial. 40: 770- 776. heavy metal contamination problems. For example, the bio- GIBBS,R. J. 1973. Mechanisms of trace metal transport in rivers. accumulation sf ""~n by crayfish in the 8978 study was Science (Washington, DC) 180: 71 -73. eightfold higher in the enclosure with a sealed plastic bottom Hmi, J. D. 1972. Chemistry and occurrence of zinc and cadmium than in the enclosure with natural lake sediments. Apparently, in surface water and groundwater. Water Resour. Res. 8: binding of "'~n to resuspended sediments, or to particles at the 661 -679. sediment- water interface of the enclosure with natural sedi- 1976. Geschemicd controls on lead concentrations in ments, effectively inhibited zinc bisaccumulation. stream water and sediments. Geochim. Cosmochina. Acta 40: 599 - 609. Before sediment resuspension is used as a remedial mea- HESSLEIN,W. H., Mi. S. BROECKER,AND D. W. SCHINDLER.1980. sure for Hg pollution, several potential problems should be Fates of metal radiotracers added to a whole lake: sediment- considered. First, although pearl dace growth was not signifi- water interactions. Can. 9. Fish. Aquat. Sci. 37: 378-386. cantly reduced in the 1979 experiment, the effects of in- HUCKABEE,J. W., J. W. ELW~D.AND S. G. HILBEBRAND.1979. creasing suspended sediments on fish productivity should be Accumulation of mercury in freshwater biota. Pn J. 0.Nriagu further investigated. Second, a safe ratio of clean to con- [ed.] The biogeochemistry of mercury in the environment. taminated sediments should be determined. The 1978 experi- Elsevier/North-Holland Biomedical Press, New York, NY. ment using Hg-polluted Clay Lake sediments and the Iabora- 696 p. JACKSON,K. S., 1. W. JONASSON,AND G. B. SKIPPEN.1978. The tory experiments of Lindberg and Hmiss (1977) suggest hat nature of mepals-sediment-water interactions in freshwater resusvnsiaan and downstream deposition of some cesntala~i- bodies. with emphasis on the role of organic matter. Earth-Sci. nated sediments might wat be a problem. Third, the possibility Rev. 14: 97- 146. that Hg attached to suspended particles could be released JACKSON,T. A. 1979. Relationships between the properties of heavy downstream in response to changes in pH, ionic strength, or metals and their biogeochemical behavior in lakes and river- chloride concentrations should be considered. For example, lake systems, p. 457-460. Proceedings of the international Hg adsorbed to kaolikee, bentonite, illite, and iron oxide at conference on management and control of heavy metals in the neutral pH is greater than 50% desorbed between pH 4.5 and environment. CEP Consultants Ltd., Edinburgh. R. 5.0 and is at least 75% desorbed at pH 4.0 (Andersson 1979). JACKSON,T. A., J. W. PARKS,P. D. JONES, N. WOYCHUK,B. A. Sermo~.AND 6. D. HOLLINGER.1984. Dissolved and suspended While such downstream changes are not expected in the mercury species in the Wabigoon River (Ontario, Canada): English-Wabigoon River system, this possibility should be seasonal and regional variation. Pn R. I. Allan and T. Brydges fully investigated for other aquatic systems. [ed.] Mercq pollution in the Wabigoon- English River system of northwestern Ontario, and possible remedial measures. Avail- Acknowledgments able from T. A. Jackson, National Water Research Institute. Winnipeg, Man. We thank F. A. J. Amstrong, G. J. Bmnskill, J. F. Klaverkamp, JACKSON,T. A., AND R. N. WOYCHUK.1986). The geochemistry D. W. Schindler, W. E. Hecky, P. Campbell, A. L. Hamilton, and distribution of mercury in the Wabigoon River system. Pn T. A. Jackson, and J. W. Parks for their advice and consmetive Mercury pollution in the Wabigosn-English River system of criticism during the preparation sf this manuscript. A. Swick md northwestern Ontario, and some possible remedial measures. A. Fumtani skillfully carried out numerous chemical and biological Interim report submitted to the Wabigoon- English R~vermer- analyses. B. E. Townsend, A. Swick, C. Johnston, C. Simonson, cury study steering committee. Available from T. A. Jackson, J. Simpson, and B. Corbett assisted with enclosure constmstion, National Water Research Institute, Winnipeg, Man. maintenance, and sampling. W. Hesslein, P. Wilkinson, E. Slavieek, J~coes,L. Mi., AND D. R.KEENEY. 1974. Methyl mercury formation and E. Bums-Flett kindly advised and assisted us with gamma isotope in mercury-treated river sediments during En siru equilibration. methodologies. M. Capel did particle size analyses. M. Stainton J. Environ. Bud. 3: 121 - 126. and co-workers camied out water chemistry analyses. A. Lutz and JONASSON,I. R. 1978. Mercury in the natural environment: a review co-workers analyzed water and sediment biota samples for total rand of recent work. Geological Smey of Canada. Paper 70-57. methyl mercury concentrations. This research was jointly funded by KARICKHOFF,S. W., AND B. S. BROWN.1978. Paraquat sorption as RUDD AND TURNER: SUPPRESSION OF ~g BIOACCUMULATION BY SEDIMENTS 2227

a function of particle size in natural sediments. 1. Environ. Qual. R~DD,J. W. M., AND M. A. TURNER.1983. The English- Wabigoon 7: 246-252. River system: air. Mercury and selenium bioaccumulation as a KLEIN.D. H., A. w.ANDREN, AND N. E. BOLTON.1975. Trace function of aquatic primary productivity. Can. J. Fish. Aquat. element discharges from coal combustion for power prduction. Sci. 40: 2251-2259. Water Air Soil Pollut. 5: 7 1 - 77. Rum, %.W. M.. h.a. A. TURNER,A. FURUTANB,A. SWICK,AND L~NDBERG,S. E., AND R. 67. HARRISS.1977. Release sf mercury B. E. TOWNSEND.1983. The English- Wabigoon River system: and organics from resuspended near-shore sediments. 9. Water I. A synthesis of recent research with a view towards mercury Pollut. Control Fed. 49: 2479- 2487. amelioration. Can. 9. Fish. Aquat. Sci. 40: 2206-2217. C~KWOOD,R. A., AND H(. Y.CHEN. 1974. Adsorption of Hg(I1) by RUDD,J. W. M., M. A. TURNER,B. E. TOWNSEND,A. %WICK,AND ferric hydroxide. Environ. Lett. 6: 15 1 - 166. A. FURUTANI.1980b. Dynamics of selenium in mercury- MCKEAGUE,J. A. 8978. Manual on soil sampling and methods of contaminated experimental freshwater ecosystems. Can. J. Fish. analysis. 2nd ed. Canadian Society of Soil Science, Ottawa, Aquat. Sci. 37: $48-857. Ont. 1988~.Mechanisms sf movement of mercury into aquatic OLSON,B. H., AND R. 6. COOPER.1974. In siru methylation of biota and a preliminary examination of some amelioration mercury in estuarine sediment. Nature (Lamdon) 252: 682 - 683. procedures. In Mercury pollution in the Wabigoon-English PARKS,J. W., J. D. HOLLMGER,AND P. M. ALMOST.1980. The Wiver system of northwestern Ontario, and possible remedial transport and dynamics of mercury in the Wabigoon Wiver and measures. Interim report to the Wabigoon-English River Clay Lake. In Mercury pollution in the Wabigmn-English mercury study steering committee. Available from J. W. M. River system of northwestern Ontario, and possible remedial Rudd, Freshwater Institute, Winnipeg, Man. measures. Interim report submitted to the Wabigoon - English SCHINDLER,D. W. 1969. Two useful devices for zooplankton and River mercury study steering committee. Available from J. W. water sampling. J. Fish. Res. Board Can. 26: 1948- 1955. Parks, OME, Thunder Bay, Ont. STAINTON,M. P., h3. J. CAPEL,AND F. A. J. ARMSTRONG.1977. The PARKS,9. W., %.A. SUTTON,AND J. D. HQLLHNGER.1984. Mercury chemical analysis of freshwater. 2nd ed. Fish. Mar. Sen. Misc. contamination of the Wabigoon/English/Winnipeg Wiver sys- Spec. hbl. 25. tem, 1980 - Causes, effects and selected remedial measures. In TESSHBR,A., P. G.C. CAMPBELL,AND M. BISSQN.1980. Trace metal R. J. Allan and T. Brydges [ed.] Mercury poilution in the speciation in the Yamaska and St. Hranqois Rivers (Quebec). Wabigoon-English River system of northwestern Onado, and Can. J. Earth Sci. 17: 90- 105. possible remedial measures. Available from J. W. Parks, OME, TOPPING,G., AND 1. M.DAVIBS. 198 1. A$ethylmercury production in Thunder Bay, Ont. the marine water column. Nature (London) 298: 243-244. POPP~C. J~,AND F. LAQUER.1980. Trace metal transport and TURNER,M. A., AND J. W. M. RUDD.l 983. The English- Wabigoon partitioning in the suspended sediments of the Rio Grande and Wiver system: III. Selenium in lake enclosures: its geochemistry, tributaries in central New Mexico. Chemosghere 9: 89-98. bioaccumulatirsn, and ability to reduce mercury bioaccumula- RUDD, 9. W. h'f., A. F~UTANI,AND M. A. TURNER.1980a. aion. Can. J. Fish. Aquat. Sci. 40: 2228-2240. Mercury methylation by fish intestinal contents. Appl. Environ. WELCH,P. S. 1948. Limnological methods. McGi-aw-Hill Book Microbial. 40: 777 -782. Company Inc.. New York, Toronto, and London. 38 1 p.