Application of radiotracer methodology for understanding the influence of geochemical fractionation on metal bioavailability in estuarine sediments Nicholas Fisher and Zofia Baumann School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York USA
Why study sedimentary metal bioavailability? • Coastal sediments are enriched with toxic metals (relative to overlying water) Kd [L kg -1 ] Location As Cd Cr Mare Island 9.12 x 10 2 4.61 x 10 3 3.08 x 10 5 Baltimore Harbor 2.41 x 10 4 5.94 x 10 3 9.52 x 10 5 Elizabeth River 2.24 x 10 2 0.90 x 10 2 4.01 x 10 4 • Potentially important source of metals to marine organisms • Conduit for animals higher in the food chain, including humans
BH MI ER MI – Mare Island in San Francisco Bay, CA; BH – Baltimore Harbor, MD; ER – Elizabeth River, Norfolk, VA
Objectives 1. To compare the relative importance of aqueous and dietary sources of metal ( 73 As, 109 Cd and 51 Cr) for the polychaete Nereis succinea 2. To study the geochemical fractionation of metals in estuarine sediments and relate these to metal assimilation in Nereis succinea 3. To study chemical composition of the gut fluid, its extracting capabilities for particle- associated metals, and its influence on metal assimilation into tissues
Radiotracer approach • Gamma – emitting radioisotopes: 73 As, 109 Cd and 51 Cr • Used in low concentrations << 0.01% of background metal concentrations • Quick, accurate and non-destructive analysis, well-suited for kinetic studies of metal uptake and release in different compartments convenience + low biological variability!
Radiolabeling of worm food WORM FOOD Radiolabeled algae Sediment + algae Thalassiosira pseudonana Sediment + dissolved centric diatom isotope Goethite + dissolved 73 As isotope 109 Cd 51 Cr Dissolved radioisotopes
Pulse-chase feeding experiments to determine AE and k ef 2 30 2 30 Food: fresh algae, goethite, and sediment with or without added radiolabeled algae, aged for 2 & 30 days Well-type NaI gamma detector
Assimilation efficiencies in Nereis succinea Unamended sediments Sediments mixed with algae 2 d 30 d 2 d 30 d ER 1.2 ± 1.05 nd 69.7 ± 9.7 16.8 ± 4.1 BH 7.8 ± 6.2 6.59 ± nd 51.6 ± 11.6 30.1 ± 1.4 < 3-70x from sediments mixed 73 As MI 10.2 ± 6.8 12.1 ± 12.5 50.7 ± 9.0 24.0 ± 12.2 with algae algae 72.41 ± 3.30 goethite 2.48 ± 0.68 ER 30.8 ± nd 43.6 ± 16.4 9.9 ± 3.5 21.5 ± 6.1 BH 1.5 ± 1.29 2.4 ± nd 68.7 ± nd 21.6 ± 14.9 no consistent pattern 109 Cd MI 46.1 ± 18.7 58.9 ± 6.6 9.4 ± 4.0 7.6 ± 4.6 algae 22.91 ± 19.73 goethite 24.15 ± 1.78 ER 4.5 ± nd 1.0 ± 0.5 0.9 ± 0.2 3.6 ± 1.7 BH 4.2 ± 3.3 4.6 ± nd 1.2 ± nd 0.8 ± 1.0 unamended sediments = sediments 51 Cr MI 4.0 ± 3.1 0.7 ± 1.3 5.0 ± 2.7 0.3 ± 0.6 mixed with algae algae 2.8 ± 1.6 goethite 34.2 ± 6.5
Biokinetic model k AE IR u C C C ss w f k g k g ew ef from water: from food: k AE IR u C C C C ss , f f ss , w w k g k g ef ew , C ss f % dietary 100 % C ss Wang et al. 1996
Dietary metal contribution to bioaccumulation age AE from food from water dietary location metal µg g -1 ng g -1 days % % 2 7.8 23.1 0.12 100 As unamended sediment 30 6.6 34.7 0.12 100 2 1.5 0.3 0.0005 100 BH Cd 30 2.4 0.4 0.0005 100 2 4.2 113.0 0.007 100 Cr 30 4.6 149.6 0.007 100 ~100% from food! As 2 1.2 1.0 173.1 85.5 2 30.8 0.4 0.17 100 Cd ER 30 43.6 1.1 0.17 100 2 4.5 15.9 0.37 100 Cr 30 1.0 86.8 0.37 100 2 10.2 0.6 1.76 99.7 As 30 12.1 0.7 1.76 99.8 2 46.1 25.0 0.002 100 MI Cd 30 58.9 9.0 0.002 100 2 4.0 88.6 0.02 100 Cr 30 0.7 14.7 0.02 100
Dietary metal contribution to bioaccumulation age AE from food from water dietary location metal µg g -1 ng g -1 days % % 2 51.6 112.1 0.12 100 As 30 30.1 65.5 0.12 100 2 68.7 0.6 0.00 100 BH Cd sediment with algae 30 21.6 0.1 0.00 100 2 1.2 29.9 0.01 100 Cr 30 0.8 86.0 0.01 100 ~100% from food! 2 69.7 15.3 173.1 98.9 As 30 16.8 6.6 173.1 97.4 2 9.9 2.0 0.9 100 ER Cd 30 21.5 0.2 0.2 99.9 2 0.9 154.9 0.4 100 Cr 30 3.6 59.6 0.4 100 2 50.7 5.7 1.76 100 As 30 24.0 5.7 1.76 100 2 9.4 10.2 0.002 100 MI Cd 30 7.6 12.3 0.002 100 2 5.0 61.6 0.02 100 Cr 30 0.3 32.4 0.02 100
extraction conditions phases intended to sediment extract 2 g wet wt 1 M MgCl 2 pH=7; 1h exchangeable 1 M NaOAc pH=5; 1h carbonate 0.5 M HCl; 30 min acid volatile sulfides Hydroxylamine/ NaOAc; 6 h @ 96 ° C Fe/Mn oxides 1 M NaOH; 8 h @ 80 ° C organic I 5 M H 2 SO 4 ; 6 h organic II residual 11 M HNO 3 ; 2 h sediment pyrite Cutter et al., in prep.
Baltimore Harbor Elizabeth River Mare Island 100 80 As 60 organic 40 20 0 100 80 Cd % 60 “carbonex” 40 20 0 100 pyrite 80 60 oxides Cr 40 AVS 20 0 2d 30d 90d algae 2d 30d 90d algae 2d 30d 90d algae
Baumann and Fisher, 2011 80 60 AE [%] 40 20 0 Linear regression, p <0.05 0 20 40 60 80 100 % in exchangeable + carbonate fractions Data for all sites, treatments, metals combined
Baumann and Fisher, 2011 50 40 30 AE [%] 20 10 0 Linear regression, p <0.05 10 20 30 40 50 60 70 80 % of metal in oxides (AVS + Fe/Mn oxides) Data for sediments labeled by algae from all sites and metals combined
Regression of assimilation efficiency and extracted fraction of metal (all sites, treatments, metals combined) exchangeable 0.4 + carbonate = “carbonex” exchangeable slope of regression exchangeable 0.2 carbonate + carbonate + AVS 0.0 pyrite pyrite + residue oxides -0.2 + AVS organic II oxides -0.4 1 2 3 4 5 6 7 8 9 10 11 12 13 single & combined fractions Baumann and Fisher, 2011
NEW Geochemical biokinetic model k z b IR u i i C C C ss w f k g k g ew ef from water: from food: z b IR k i i C C u C C ss , f f ss , w w k g k g ef ew z i - % of metal in fraction “i”; b i - slope of regression between AE and z i
Metal concentrations in worms; model predictions vs. field measurements (all sites and metals) Directly labeled Algae labeled carbonex total
Chemical composition of the gut fluid gut fluid: seawater ratio 2400 Cl - 0.9 2- 5.7 SO 4 2300 10.1 K + mmol kg -1 Na + 4.9 2200 Ca 2+ 4.5 600 Mg 2+ 5.0 400 200 0 gut fluid seawater gut fluid pH= ~7; [AA] = 2.46 mg L -1
Amino acid composition of gut fluid and bovine serum albumin gut fluid (GF) BSA % of total Amino Acid BSA : GF mean ± SD mean ± SD % of total AA in gut [g/g] [mmol/L ] [mg/L] AA in BSA fluid Alanine 3.891 ± 0.231 0.35 ± 0.02 14.2 0.082 6.6 0.5 Arginine 1.244 ± 0.017 0.22 ± 0.00 8.9 0.6 0.069 5.6 Aspartic Acid 8.1 8.2 1.0 1.466 ± 0.385 0.20 ± 0.05 0.102 γ -Aminobutyric Acid - 0.010 ± 0.017 0.001 ± 0.002 0.04 - - Glutamic Acid 9.8 0.2 1.641 ± 0.199 0.24 ± 0.03 0.024 2.0 Glycine 8.9 0.3 2.984 ± 0.239 0.22 ± 0.02 0.029 2.3 Histidine 10.9 2.4 0.714 ± 0.151 0.11 ± 0.02 4.5 0.135 Isoleucine 2.955 ± 0.649 0.39 ± 0.09 15.9 0.0356 2.9 0.2 Leucine 1.161 ± 0.055 0.15 ± 0.01 14.4 2.4 6.1 0.179 Lysine 0.758 ± 0.538 0.11 ± 0.08 15.7 3.5 4.5 0.195 Methionine 0.0 0.119 ± 0.206 0.02 ± 0.03 0.8 0.000 0.0 Phenylalanine 8.3 2.6 0.488 ± 0.042 0.08 ± 0.01 3.3 0.103 Serine 0.8 1.281 ± 0.018 0.13 ± 0.00 5.3 0.052 4.2 Threonine 1.2 0.941 ± 0.102 0.11 ± 0.01 4.5 0.067 5.4 Tyrosine 3.5 0.257 ± 0.022 0.05 ± 0.00 2.0 0.089 7.2 Valine 0.693 ± 0.011 0.08 ± 0.00 3.3 0.078 3.3 1.0 Σ AA 20.6 mmol L -1 2.46 mg L -1 1.24 2 BSA data from Shi et al., 2006
Release of 73 As from particles to solution sediment sediment goethite + + + algae dissolved dissolved isotope isotope 70 25 % 73As released 60 15 20 50 15 10 40 30 10 5 20 5 10 0 0 0 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 hours water BSA BSA + Cl- gut fluid assimilation efficiency
Summary 1.Nearly all of bioaccumulated metal ( >98%) comes from diet. 2.Sedimentary metals in the easily extractable pool (“carbonex”) are most bioavailable for polychaetes; metals associated with iron oxides are not readily bioavailable. 3.Metal release from ingested particles into gut fluid is a necessary but not sufficient step to explain metal assimilation in worms.
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