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Bioaccumulation: aquatic / sediment

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SrS will not occur as such in the environment. In the aqueous and terrestrial environment, strontium sulfide dissolves in water releasing strontium cations and sulfide anions. 

Key value for chemical safety assessment

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SrS will not occur as such in the environment. In the aqueous and terrestrial environment, strontium sulfide dissolves in water releasing strontium cations and sulfide anions.

Sulfide:Twelve studies were identified on bioconcentration/bioaccumulation of sulfide in aquatic organisms. Of these studies, seven were considered reliable with restrictions (Klimisch 2). All reliable studies were studies on marine aquatic invertebrates. Reliable data are not available for freshwater invertebrates and freshwater or marine fish and algae. Wet-weight based BCF values for total sulfide ranged from none (sulfide was not detectable in the organisms, Laudien et al., 2002) to 1.6 L/kg ww (Jahn and Theede, 1997). Dry-weight based BCF values amounted to 7.5 L/kg dw (Jahn et al., 1996). In most studies concentrations of other sulfide species such as thiosulfate, sulfite, sulfate, and elemental sulfur were also monitored in the test organisms. Apparently, sulfide entering the organisms is quickly oxidized to thiosulfate. Available studies indicate that sulfide does not have a potential for bioconcentration/bioaccumulation. All reliable studies were applied in a weight-of-evidence approach. The highest wet-weight based BCF value of 1.6 (Jahn and Theede, 1997) was selected as key value for bioconcentration. This value originates from a study in which adult bivalves (Macoma balthica) were exposed for 6 days to a single sulfide concentration of 6.4 mg S2-/L in a 3-day static renewal hypoxic system. The type of tissue analyzed was not specified but most likely represents either whole organisms or soft tissue.

Strontium: As reactive electropositive metal, strontium is easily oxidized to the stable and colourless Sr2+ion in most of its compounds, the chemical behaviour resembling that of calcium and/or barium (Wennig and Kirsch, 1988). In the environment, the element only occurs in one valence state (Sr2+), does not form strong organic or inorganic complexes and is commonly present in solution as Sr2+(Lollar, 2005). Consequently, the transport, fate, and toxicity of strontium in the environment are largely controlled by solubility of different Sr-salts (e. g., SrCO3, Sr(NO3)2, SrSO4, …).

These findings are sufficient justification for the implementation of a read-across strategy with ecotoxicity results obtained in tests that were conducted with different strontium compounds that generate free Sr2+-ions in solution.

When evaluating and interpreting uptake and bioaccumulation data for strontium, it is important to realize that due to the similarity between calcium and strontium, a major part of the absorbed strontium is transported into the bones.Suzuki et al (1972)reported the distribution of strontium in fish. Sr-levels were determined in dry ash (i.e., not converted toμg/g dry wt). The data indicated that approximately 5% of total strontium was present in muscle, visceral organs and digestive tract. More than 94% of strontium was found in so-called hard tissues (e.g., bones, scales, fins).

For the evaluation secondary poisoning and the transport of strontium through the food chain, concentration levels and concentration factors in soft tissues are more relevant than in hard tissues like bones and shells.

Several authors reported relevant bioaccumulation data for strontium to aquatic organisms. One of the earliest studies was conducted byWebb (1937) who determined the Sr-content in seawater and in 24 different marine organisms (gastropods, lamellibranchia, echinoderms, fish, crustaceans, algae, palychaetes and Nemertea and Urochordata). Concentrations were expressed as % dry ash. The dry ash percentage of seawater was 0.1%, with Sr being the 5th most abundant cationic element in seawater after Na (84%), Mg (10%), and Ca/K (each approx. 3%). Strontium percentages in dry ash of marine were situated between 0.015% and 2% of the total ash content, with most values below 1% (exceptions: mantle of the gastropodArchidoris britannica(2%) and the disc of the echinodermOphiocomina nigra(1%)). Based on these dry ash percentages can be concluded that strontium accumulation by marine organisms is generally situated between 0.15 and 20%. 

Moiseenko and Kudryavtseva (2001) investigated strontium levels in several soft tissues of white fish (Coregonus lavaretus), brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus). Fish were collected at five different zones, but strontium data were only available for zone III, V and VI. Strontium levels in the water for each zone were 9 (5-26)μg/L, 66 (50-220)μg/L and 16 (4-50)μg/L, respectively. Pooling all fish species and sampling locations together, the BAF for liver was situated between 21.3 and 74.4. Average muscle Sr-concentrations were situated between 0.5 and 5.4μg/g, resulting in BCFs situated between 7.6 and 91.1 (n=6), except for brown trout caught at Zone III (BAF of 396.6). No relationship was noted between water concentration and Sr-muscle concentration.

Mean Sr-levels in the skeleton were markedly higher, i.e., ranging from 125 to 690μg/g, and BAFs were situated between 2273 and 14111. High BAF values were also found for gills with mean values between 1136 and 11888.  

Brown trout was the only species caught at three locations, thus allowing the investigation of the relationship between Sr-levels in the water and Sr-levels in different tissues. Data were available for three tissues (muscle, skeleton and gill), and showed for all three Sr-levels (66, 16 and 9μg/L) similar internal Sr-concentrations (muscle: 0.5-3.56μg/L; skeleton: 127-171μg/L; gill: 75-108μg/g). Consequently, a decrease of the BAF is noted with increasing Sr-concentration in the water. These data support the hypothesis that fish are able to maintain a rather constant concentration of Sr in their body. A decrease of the muscle and skeleton BAF with increasing Sr-level in the water was also noted for the white fish, although data were only available for 2 concentration levels (66 and 16μg/L). 

Stanek et al (1990) investigated the uptake of90Sr (added as SrCl2) in a simplified 22d experimental aquatic system, containing sediment, algae (Cladophora glomerata), invertebrates (gastropodPlanorbius corneus) and fish (Cyprinus carpio). Reported accumulation coefficients were 115 for algae and 143 / 3 for the soft tissues of gastropods / fish, respectively. Equilibrium for algae was reached within 1 day, indicating once more that this is a rapid adsorption process rather than an actual uptake process. Stanek et al (1990) also reported bioconcentration factors in shells and bones. Accumulation coefficient for the shell of the gastropod was 356, and high levels were also noted in the bones and scales of the fish (152 and 68, respectively).

Ueda et al (1973) measured Sr-levels in 241 samples of 63 marine species, covering fish, crustaceans, echinoderms and algae. For each organism the concentration factor was derived, using a default concentration level of 8 mg/L. This value is considered as a typical concentration for Sr in the marine environment (Culcin, 1965; Angino et al, 1966; Nagaya et al, 1970). An overview of the different concentration factors for the soft parts and hard parts of different taxonomic groups is presented below:

-         Fish flesh (5 species): Sr-range was 1.2-3.5 mg Sr/kg raw ; Concentration factor ranging from 0.2 to 0.4;

-         Echinodermata/coelenterata (6 species): Sr-range was 5-848 mg Sr/kg raw ; Concentration factor ranging from 0.7 to 106;

-         Algae (9 species): Sr-range was 2-250 mg Sr/kg raw ; Concentration factor ranging from 0.3 to 31;

-         Fish bone (17 species): Sr-range was 78-293 mg Sr/kg raw ; Concentration factor ranging from 10 to 37;

-         Exoskeleton of crustacea (12 species): Sr-range was 278-1470 mg Sr/kg raw; Concentration factor ranging from 35 to 184;

-         Shell of mollusca (12 species): Sr-range was 17-1601 mg Sr/kg raw; Concentration factor ranging from 2 to 200;

Bologa (1984) studied the uptake of radioactive Sr (85SrCl2) by the musselMytilus galloprovincialisand the clamMya arenaria, and reported Sr concentration factors (CF) in soft parts, hard parts and siphon after an exposure period of 20-105 days for the mussel, and 20-41 days for the clam. For the musselM. galloprovincialisthe CF ranged between 1 and 5 for the soft parts. Similar values were found forM. arenaria, where the CF range was 1-6 and 2-11 for the soft parts and siphon, respectively. The CF for the shell of the musselM. galloprovincialisranged between 2 and 11. Similar values were found forM. arenaria, where the CF range was 3-17 for the shell. 

Nakamoto and Hassler (1992) investigated whether elements (incl. strontium) accumulated in bluegills (Lepomis macochirus) affected growth and fecundity. Sr-concentrations (filtered fraction) in water samples from the Merced river and Salt Slough were 138μg/L (range: 100-182μg/L) and 1,106μg/L (range: 666-1,535μg/L), respectively, and were measured by Argon ICP-AES (detection limit: 1μg/L).

For the male and female bluegills that were caught in the Merced River, the tissue concentration levels of Sr in carcasses (whole body) were 151μg/g dw (range: 109-172μg/g dw) and 188μg/g dw (range: 146-256μg/g dw), respectively. The average internal concentration in the gonads of the bluegills from this area was more than one order of magnitude lower, i.e., 3.6-4.9μg/g dw for male and female fish, respectively.

Similar observations were made for the fish caught at Salt Slough. Carcass concentrations levels were 183.3μg/g dw (range: 162.0-195.0μg/g dw) and 207.2μg/g dw (range: 134.0-267.0μg/g dw) for male and female organisms, respectively. Here too, gonad levels were more than one order of magnitude lower (5.0-5.7μg/g dw).

Reported bioconcentration factors for the carcass and gonads of the sampled female fish were 60.6-342.7 and 1.5-11.9, respectively. The BCFs for the carcass and gonads of male fish were 92.0-40.3 and 1.4-7.5, respectively. Comparable BCF-values for the carcass were determined for different other metals (Cr, Cu, Mg, Mn, V).

A number of authors only provided internal concentrations of Sr in soft tissues, hard tissues or whole-body concentrations. For all of these data no BAF values could be derived as no Sr-levels in water were reported:

-         Hellou et al (1992a) reported Sr levels in the muscle, liver and ovaries of cod (Gadus morhua) collected in Northwest Atlantic (Divisions 2J and 3Ps of NAFO) off the coast of Newfoundland. Mean Sr-level in the muscle tissue were 2.23±0.7 and 2.76±0.9μg/g dry wt for 2J and 3Ps, respectively. Levels in the liver were 0.73±0.07 and 0.94±0.29μg/g dry wt, and levels in the ovaries were 5.61±0.5 and 3.73±0.91. In a second study by the same author (Hellou et al, 1992b), a Sr tissue concentration of 0.66μg/g dry wt (range: 0.17-4.52μg/g) was reported in the muscle tissue of another fish, the bluefin tunaThunnus thunnus.

-         Internal concentrations of strontium in the egg yolks of the marine vertebrateCaretta caretta(loggerhead sea turtle) were reported byStoneburner et al. (1980) (In:Meyers-Schöne and Walton, 1994), and were situated between 66.1 and 74.0μg/g wet weight. As no external concentrations or dry weight values were reported, it was not possible to derive an indicative BCF with this data. Moreover, it is not clear to what extent concentration levels in yolk are relevant for overall body concentrations. Indeed, for several other metals (e.g., copper, zinc, lead), the concentrations in yolk were significantly higher compared to other fractions of the body.

-         Hinck et al (2008)collected bass (n=1003) and carp (n=1605) form 96 sites on major US rivers and determined metal content in whole body composite samples. Median Sr-levels in female and male bass were 14.7 and 13.8μg/g wet weight, respectively. Similar median Sr-levels were found in female and male carp, ie., 15.6 and 15.7μg/g wet weight, respectively. Bass feed primarily onsh, whereas carp forage for aquatic insects and plants in sediments. The higher trophic status of bass compared to carp typically results in bass having greater concentrations of bioaccumulative contaminants. As levels in bass and carp were similar, strontium should not be considered as a potential bioaccumulative compound.

-         Some other authors reported Sr-levels in field-collected fish, but measured levels were only relevant for the whole-body concentration, i.e., no analysis on specific organs or tissues were conducted. Sr-levels in juvenile striped bass from the San Joaquin Valley and San Francisco area (California) ranged from 18 to 200μg/g, with a geometric mean of 50.4μg/L (n= 55, representing 22 locations) (Saiki and Palawski, 1990). This mean value is in line with the range of 96-450μg/g as reported byRadtke et al (1988)for adult common carp from the Lower Colorado River Valley.Schroeder et al (1988)found similar concentrations in a mixture of common carp, mosquitofish and yellow bullheads, i.e., a range of 46-200μg/g. Neither of these studies provided measured Sr-levels in the water column.

-         Samples of sediment and fish (slenderhead darterPercina phoxocephala, common carpCyprinus carpioand smallmouth buffaloIctiobus bubalus) were collected in 1991-1992 from the Neosho River drainage, and Sr-content was determined (Allen et al, 2001). Sr-levels in the sediment were situated between 27 and 107 mg/kg dw. Whole-body concentrations in the fish were 89-115 mg/kg dw, 58-195 mg/kg dw and 80-214 mg/kg dw forP. phoxocephala,C. carpioand I. bubalus, respectively. In this study, mussel samples were also taken (the monkeyfaceQuadrula metanervaand pimplebackQuadrula pustulosa) and analysed.. Concentration levels inQ. metanervaandQ. pustulosawere 253-429 mg/kg dw and 144-311 mg/kg dw, respectively. These values were significantly higher compared to the data that were generated for fish in this study (see robust study summary). 

Conclusion

-         Concentration factors of strontium in soft parts of fish (muscle, gonads) generally ranged between 0.2 and 91.9 (Moiseenko and Kudryavtseva, 2001; Nakamoto and Hassler, 1992; Ueda et al, 1973; Stanek et al, 1990); concentration factors for algae were situated between 0.3 and 115 (Ueda et al, 1973; Stanek et al, 1990). Lowest values were found for marine species, but the ambient concentration of Sr in marine water (8 mg/L) is markedly higher than levels in the freshwater compartment (μg-range).

-         Higher concentration factors were found in hard body parts (bones, shell): values ranges between 10 and 14111 for fish bones and between 2 and 200 for shells of molluscs (Moiseenko and Kudryavtseva, 2001; Ueda et al, 1973; Stanek et al, 1990; Bologa, 1984)

-         Concentration levels of Sr in soft tissues of fish (muscle, flesh, gonads & ovary, liver) were situated between 0.5 and 5.6μg/g dry wt (Hellou et al, 1992a, 1992b; Moiseenko and Kudryavtseva, 2001; Nakamoto and Hassler, 1992; Ueda et al, 1973) ; Whole body concentrations (incl. bones) ranged from 18 to 450μg/g (Nakamoto and Hassler, 1992; Hinck et al, 2008;Saiki and Palawski, 1990; Radtke et al, 1988; Schroeder et al, 1988; Allen et al, 2001); Levels in bones were found between 78 and 690μg/g (Moiseenko and Kudryavtseva, 2001; Ueda et al, 1973).

-         Moiseenko and Kudryavtseva (2001) noted for fish a decrease of the BAF with increasing Sr-concentration in the water (9, 16, 66μg/L). These data support the hypothesis that fish are able to maintain a rather constant concentration of Sr in their body. A decrease of the muscle and skeleton BAF with increasing Sr-level in the water was also noted for the white fish, although data were only available for 2 concentration levels (66 and 16μg/L).

References:

Allen, G.T. et al.(2001): Metals, Boron, and Selenium in Neosho Madtom Habitats in the Neosho River in Kansas, U.S.A., Find out how to access preview-only contentEnvironmental Monitoring and AssessmentJanuary 2001, Volume 66,Issue 1, pp 1-21

Hellou, J.; et al. (1992): Heavy metals and other elements in three tissues of Cod, Gadus morhua from the Northwest Atlantic, Marine Pollution Bulletin 24, 452-458

Hinck, J.E. et al.(2008): Relations between and among contaminant concentrations and in black bass (Micropterus Spp.) and common carp (Cyprinus carpio) from large U.S. rivers, 1995 -2004, J. Environ.Monit., 2008, 10, 1499 -1518

Radtke D. B. et al.(1988): Reconnaissance investigation of water quality, bottom sediment and biota associated with irrigation drainage in the lower Colorado River Valley. Arizona. California, and Nevada, 1986-1987. U.S. Geological Survey Water·Resources Investigations Report 88·4002. Tucson. Arizona

Saiki, M.K., Palawski, D.U. (1990): Selenium and other elements in juvenile striped bass from the San Joaquin Valley and San Francisco Estuary, California,Archives of Environmental Contamination and ToxicologySeptember–October 1990, Volume 19,Issue 5, pp 717-730

Schroeder. R. A. et al (1988): Reconnaissance investigation of water-quality, bottom sediment, and biota associated with irrigation drainage in the Tulare Jake bed area, southern San Joaquin Valley. California. 1986-1987. Water-Resources Investigations Report 88-4001. U.S. Geological Survey Sacramento, California.

Stoneburner, D.L. et al. (1980) Heavy metals in loggerhead sea turtle eggs (Caretta caretta): Evidence to support the hypothesis that demes exist in the western Atlantic population. J Herpetol 14:171–175.

Suzuki, Y.; et al. (1972): Accumulation of strontium and calcium in freshwater fishes of Japan, J. Radiat. Res. 13, 199-207

Webb, D.A. (1937): Studies on the ultimate composition of biological material. Part II: Spectrographic analyses of marine invertebrates, with special reference to the chemical composition of their environment, Scient.Proc. R.D.S. 21, 505-539

Wennig, R.; Kirsch, N. (1988): Chapter 57 Strontium, In: Seiler, U. G. et al.(eds), Handb. Tox. Inorg. Comp. NY, 631-638