Strontium

Bioaccumulation: aquatic / sediment

Description of key information

Available data indicate that the bioconcentration and bioaccumulation of strontium is negligible: internal concentrations of soft tissues range from 0.5 to 5.7 μg/g regardless of external concentrations (9 – 8000 μg/L). Whole body concentrations are considered less relevant due to the potential of Sr to replace Ca in the bones. Reported tissue BAFs vary by more than 2 orders of magnitude, but remain below 100. Moreover, an inverse relationship between exposure concentration and BAF has been observed, i. e., decreasing BAFs with increasing Sr levels in the water column (Moiseenko and Kudryavtseva, 2001). The data indicate that Sr is homeostatically controlled by aquatic organisms. The homeostatic control in soft tissues of Sr seems to function up to the milligramme range of exposure (8 mg/L in seawater; Ueda et al, 1973).

Limited information on transfer of Sr through the food chain indicates that strontium does not biomagnify in aquatic food chains.

Additional information

When evaluating and interpreting the data on uptake and bioaccumulation of strontium, it is important to note that due to the similarity of calcium and strontium, a major fraction of the absorbed Sr is transported into bones. Suzuki et al (1972) reported the distribution of Sr in fish. Strontium levels were determined in dry ash (i.e., not not converted to μg/g dry wt). The data indicate that approximately 5% of total Sr was present in muscle, visceral organs and digestive tract. More than 94% of Sr was found in so-called hard tissues (e.g., bones, scales, fins). For the evaluation of secondary poisoning and the transport of Sr 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 published relevant data of the bioaccumulation of Sr in aquatic organisms. One of the earliest studies was conducted by Webb (1937) who determined the Sr concentration of seawater and 24 different marine organisms (gastropods, lamellibranchia, echinoderms, fish, crustaceans, algae, palychaetes and Nemertea and Urochordata). The relative Sr concentration of dry ash of 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%). Relative strontium concentrations of the dry ash of marine organisms ranged from 0.015% to 2% with most values being below 1% (exceptions: mantle of the gastropod Archidoris britannica (2%) and the disc of the echinoderm Ophiocomina nigra (1%)). Based on relative Sr concentrations of dry ash, it can be concluded that Sr accumulation by marine organisms is typically low and ranges in individual tissues from 0.15 and 20%. 

Moiseenko and Kudryavtseva (2001) investigated Sr-levels in severals of tissues of white fish (Coregonus lavaretus), brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus). Fish were collected at five different zones, but Sr-data were only available for zone III, V and VI. Sr-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 ranges from 21.3 to 74.4. Average muscle Sr-concentrations ranged from 0.5 to 5.4 μg/g, resulting in BCFs 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 concentrations and Sr-muscle concentrations. Mean Sr levels in the skeleton were higher, i.e., ranging from 125 to 690 μg/g, and BAFs were 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 9 μg/L) similar internal Sr-concentrations (muscle: 0.5-3.56 μg/L; , skeleton: 127-171 μg/L; gill: 75-108 μg/g). Consequently, a decrease of the BAF is observed with increasing Sr concentration of the water. These data support the hypothesis that fish are able to maintain a rather constant body concentration of Sr. A decrease of the muscle and skeleton BAF with increasing Sr level of the water was also observed in for the white fish, although data were only available for 2 concentrations (66 and 16 μg/L). 

Stanek et al (1990) investigated the uptake of⁹⁰Sr (added as SrCl₂) in a simplified 22-d aquatic experimental system, containing sediment, algae (Cladophora glomerata), invertebrates (gastropod Planorbius corneus) and fish (Cyprinus carpio). Reported accumulation coefficients amount to 115 for algae and 143 and 3 for the soft tissues of gastropods and fish, respectively. A steady-state was reached by algae within 1 day indicating also that this is a rapid adsorption process rather than an active uptake process. Stanek et al (1990) also reported bioconcentration factors in shells and bones. The 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. The concentration factor was derived for each organism using a default concentration of 8 mg/L. This value is considered as a typical Sr concentration of 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 concentrations ranging from 1.2 to 3.5 mg Sr/kg ww ; Concentration factors ranging from 0.2 to 0.4;

-         Echinodermata/coelenterata (6 species): Sr concentrations ranging from 5 to 848 mg Sr/kg ww; Concentration factors ranging from 0.7 to 106;

-         Algae (9 species): Sr concentrations rangung from 2 to 250 mg Sr/kg ww ; Concentration factors ranging from 0.3 to 31;

-         Fish bone (17 species): Sr concentrations ranging from 78 to 293 mg Sr/kg ww ; Concentration factors ranging from 10 to 37;

-         Exoskeleton of crustacea (12 species): Sr concentrations ranging from 278 to 1470 mg Sr/kg ww; Concentration factors ranging from 35 to 184;

-         Shell of mollusca (12 species): Sr concentrations ranging from 17 to 1601 mg Sr/kg ww; Concentration factors ranging from 2 to 200;

Bologa (1984) studied the uptake of radioactive Sr (85SrCl2) by the mussel Mytilus galloprovincialis and the clam Mya 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 mussel M. galloprovincialis, the CF ranged from 1 to 5 for the soft parts. Similar values were found for M. arenaria with the the CF ranging from 1 to 6 and 2 to 11 for the soft parts and siphon, respectively. The CF for the shell of the mussel M. galloprovincialis ranged from 2 to 11. Similar values were found for M. arenaria with the CF ranging from 3 to 17 for the shell. 

Nakamoto and Hassler (1992) investigated whether elements (incl. strontium) accumulated in bluegills (Lepomis macochirus) affected growth and fecundity. Strontium concentrations (filtered fraction) in water samples from the Merced river and Salt Slough amounted to 138 μg/L (range: 100-182 μg/L) and 1,106 μg/L (range: 666-1,535 μg/L), respectively.

For male and female bluegills caught in the Merced River, the tissue concentrations of Sr in carcasses (whole body) amounted to 151 μg/g dw (range: 109-172 μg/g dw) and 188 μg/g dw (range: 146-256 μg/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 - 4.9 μg/g dw for male and female fish, respectively.

 

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

Bioconcentration factors for the carcass and gonads of the sampled female fish of 60.6 - 342.7 and 1.5 - 11.9, respectively, were reported. The BCFs for the carcass and gonads of male fish amounted to 92.0 - 40.3 and 1.4 - 7.5, respectively. 

A number of authors only provided internal concentrations of Sr in soft tissues, hard tissues or whole-body concentrations. However, BAF values could not be derived from these studies since Sr levels of the water were not reported:

- Hellou et al (1992a) reported Sr levels of muscles, 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 of the muscle tissue amounts to 2.23±0.7 and 2.76±0.9 μg/g dry wt for 2J and 3Ps, respectively. Levels in the liver were 0.73±0.07 and 0.94±0.29 μg/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 0.66 μg/g dry wt (range: 0.17-4.52 μg/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 vertebrate Caretta caretta (loggerhead sea turtle) were reported by Stoneburner et al. (1980) (In: Meyers-Schöne and Walton, 1994), and ranged from 66.1 to 74.0 μg/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 13.8 μg/g wet weight, respectively. Similar median Sr-levels were found in female and male carp, ie., 15.6 and 15.7 μg/g wet weight, respectively. Bass feed primarily on fish, 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 200 μg/g, with a geometric mean of 50.4 μg/L (n= 55, representing 22 locations) (Saiki and Palawski, 1990). This mean value is in line with the range of 96-450 μg/g as reported by Radtke et al (1988) for adult common carp from the Lower Colorado River Valley. Schroeder et al (198 found similar concentrations in a mixture of common carp, mosquitofish and yellow bullheads, i.e., a range of 46-200 μg/g. Neither of these studies provided measured Sr-levels in the water column.

-  Samples of sediment and fish (slenderhead darter Percina phoxocephala, common carp Cyprinus carpio and smallmouth buffalo Ictiobus bubalus) were collected in 1991-1992 from the Neosho River drainage, and Sr concentrations were determined (Allen et al, 2001). Sr levels of the sediment ranged from 27 to 107 mg/kg dw. Whole-body concentrations of the fish amount to 89-115 mg/kg dw, 58-195 mg/kg dw and 80-214 mg/kg dw for P. phoxocephala, C. carpio and I. bubalus, respectively. In this study, mussels (the monkeyface Quadrula metanerva and pimpleback Quadrula pustulosa) were also sampled; strontium concenrations in Q. metanerva and Q. pustulosa amount to 253-429 mg/kg dw and 144-311 mg/kg dw, respectively and are higher than the concentrations measured in fish.

Conclusion

Concentration factors of strontium in soft parts of fish (muscle, gonads) range from 0.2 to 91.9 (Moiseenko and Kudryavtseva, 2001; Nakamoto and Hassler, 1992; Ueda et al, 1973; Stanek et al, 1990); concentration factors for algae range from 0.3 to 115 (Ueda et al, 1973; Stanek et al, 1990). The lowest values were measured in marine species, but the ambient Sr concentration of saltwater (8 mg/L) is higher than typical freshwater levels (μg-range).

Higher concentration factors were measured in hard body parts (bones, shell): values ranging from 10 to 14111 in fish bones and from 2 to 200 in shells of molluscs (Moiseenko and Kudryavtseva, 2001; Ueda et al, 1973; Stanek et al, 1990; Bologa, 1984).

Concentrations of Sr in soft tissues of fish (muscle, flesh, gonads & ovary, liver) were low, i.e. between 0.5 and 5.6 μg/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 450 μg/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 ranged from 78 to 690 μg/g (Moiseenko and Kudryavtseva, 2001; Ueda et al, 1973).

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