The English-Wabigoon River System: 11. Suppression of Mercury and Selenium Bioaccumulation by Suspended and Bottom Sediments
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The English-Wabigoon River 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 Canada (.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 Ontario (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.