Environ. Sci. Technol. 1997, 31, 1716-1722
Modeling the Elimination of Mercury by Fish MARC TRUDEL* AND JOSEPH B. RASMUSSEN Department of Biology, McGill University, 1205 Avenue Dr. Penfield, Montre´al, Que´bec, Canada H3A 1B1
Mass balance models can be used to predict mercury accumulation in fish. However, factors influencing mercury elimination, an essential parameter of the mass balance model, are poorly understood. We developed a general model of mercury elimination from fish using literature data. Our analysis showed that short-term experiments (95%) form of Hg in fish (47-50), we developed a general model of MeHg excretion rate by fish using multiple regression analyses (46).
Results and Discussion Statistical Analyses. A total of 96 estimates of Hg elimination rate from the slow compartment covering 16 fish species were obtained from the literature (Table 1). The elimination rate of inorganic Hg (r ) -0.88; p < 0.0001) and MeHg (r ) -0.64; p < 0.0001) were both negatively correlated to the duration of the experiment. These data were therefore separated into two groups according to the duration of the experiment for the remainder of the analyses (90 days). These time intervals were chosen because Rowan and Rasmussen (32) showed that an experiment needed to last at least 90 days to adequately distinguish the fast and slow components of 137Cs elimination. Short-term experiments (i.e., 95%) (47-50), Hg mass balance models should rely only on the clearance rate of MeHg from fish. Hendriks (35) has recently developed an empirical model of MeHg elimination using both inorganic Hg and MeHg excretion rate estimates. His model is therefore likely to overestimate the clearance rate of MeHg from fish. Furthermore, mass balance models based on his MeHg clearance model are likely to underestimate Hg concentration in fish. The predominance of MeHg over inorganic Hg in fish has generally been attributed to the higher assimilation efficiency of MeHg from food than inorganic Hg (59, 60). The assimilation efficiency of MeHg from food is 5-10-fold higher than inorganic Hg (36, 39, 61). The 3-fold difference observed between the excretion rate of these two substances suggests that both the higher assimilation efficiency of MeHg from food and the lower clearance rate of MeHg from fish are responsible for the predominance of MeHg in fish. Influence of Body Size. Excretion rates of persistent contaminants are generally negatively correlated with body size (16, 31-33, 35, 44). The negative correlation observed between MeHg excretion rate and body size in our study is thus consistent with the literature. Inorganic Hg and MeHg elimination rates obtained in short-term experiments were also negatively correlated to body size, but with much steeper slopes than in long-term experiments. The allometric exponent of MeHg clearance rate obtained in our study was equal to -0.20 (SE ) 0.06), which is identical to the value assumed by Fagerstro¨m et al. (17). The steeper slope obtained by Norstrom et al. (16), -0.58, could be attributed to the
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TABLE 1. Body Size, Water Temperature, Mercury Elimination Rate and Half-Life, Mercury Concentration ([Hg]) and Burden, and Duration of Experiment of Various Fish Species Reported in the Literature species
size (g)
Carassius auratus Carassius auratus Carassius auratus Esox lucius Esox lucius Gambusia affinis Ictalurus nebulosus Ictalurus enbulosus Ictalurus nebulosus Ictalurus punctatus Perca flavescens Pleuronectes platessaa Pleuronectes platessa Raja clavataa Raja clavata
1.3 15 10 62 208 0.3 62 208 320 250 15 42 70 18 59
Anguilla vulgaris Anguilla vulgaris Anguilla vulgaris Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Carassius auratus Esox luciusa Esox luciusa Esox luciusa Esox luciusa Esox lucius Esox lucius Esox lucius Esox lucius Esox lucius Esox lucius Ictalurus nebulosus Ictalurus nebulosus Ictalurus nebulosus Ictalurus nebulosus Ictalurus nebulosus Ictalurus nebulosus Lepomis macrochirus Lota lota Lota lota Lota lota Lota lota Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss
100 100 100 1 7 17 1 7 8 9 10 10 43 1 5 7.4 7.4 8.1 9.2 10.2 15.4 42.9 16160 18500 3920 1000 300 300 300 75 150 85 7 75 150 300 8 280 8 350 680 270 390 33 33 33 33 33 33 33 6.3 7.3 10.2 5.5 6.6 8.2
1718
9
temp (°C)
K (d-1)
half-life (d)
13 13 20 13 13 13 21 13 ‘10 10 10 10
Inorganic Mercury 0.087 8 0.046 15 0.029 24 0.01 69 0.0081 86 0.53 1.3 0.01 69 0.0081 86 0.0039 178 0.00096 723 0.046 15 0.0051 135 0.021 33 0.0029 242 0.011 62
10 10 10 13 13 13 20 20 10 5 20 20 24 22 24 22 24 10 5 20 24 24 4 10 10 10 10 10 10 13 13 9 13 13 13 13 14 19 24 13 13 10 10 17 17 17 17 17 17 4 10.5 10.5 10.5 10.5 10.5 10.5
Methylmercury 0.00076 910 0.00067 1030 0.00067 1030 0.042 17 0.017 41 0.008 87 0.035 20 0.023 30 0.021 33 0.021 33 0.02 35 0.023 30 0.019 36 0.02 35 0.013 53 0.008 87 0.013 53 0.006 116 0.006 116 0.006 116 0.006 116 0.004 173 0.0011 680 0.00072 967 0.00095 728 0.00094 737 0.00092 750 0.0011 640 0.00089 780 0.005 139 0.004 173 0.0018 385 0.017 41 0.005 139 0.004 173 0.0075 92 0.03 23 0.002 347 0.0053 130 0.0016 433 0.00098 707 0.003 231 0.002 347 0.0034 204 0.0022 316 0.0022 319 0.0022 320 0.0026 268 0.0019 348 0.0013 516 0.0065 107 0.0052 134 0.0065 107 0.0083 83 0.006 116 0.0065 106
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[Hg] (µg g-1)
burden (µg)
0.0064
1.6
0.018 0.018 0.018
1.8 1.8 1.8
0.72 0.85 0.15 0.51 0.23 0.4 0.71 0.25 8.7 7.9 8.3 8.4 0.0058 0.0058 0.0058
0.04
3 0.4 0.3 0.4 0.11 0.06 0.08
4.8 7.6 7.8
0.72 6.29 1.11 4.131 2.116 4.08 10.934 10.725 140592 146150 32536 8400 1.74 1.74 1.74
8.25
99 13.2 9.9 13.2 3.63 1.98 2.64
26.4 50.16 63.96
duration (d)
ref
28 60 60 59 59 6 70 70 70 155 60 141 41 165 43
36
130 130 130 60 60 60 60 60 60 60 60 60 60 43 45 59 41 59 59 59 59 59 180 270 365 365 130 130 130 59 59 60 61 61 61 61 60 60 95 60 60 60 60 111 124 124 124 115 125 126 28 56 84 28 56 84
51 52 36 53 36 38 39 41
26 36 37
44
54
26 36 37 36
37 25 36 37 24
55
TABLE 1 (Continued) species
size (g)
temp (°C)
Oncorhynchus mykis Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Oncorhynchus mykiss Perca flavescens Perca flavescens Perca flavescens Perca flavescens Pleuronectes flevus Pleuronectes flevus Pleuronectes platessaa Pleuronectes platessa Poecilla reticulata Raja clavata Serranus criba Stizostedion vitreum Stizostedion vitreum
5.1 6.1 7.3 6.8 10.6 17.1 5.4 7.7 12.3 5.7 8.7 13.3 9 17 9 47 180 180 61 60 0.17 107 10 12 12
10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 15 13 15 11 10 10 10 10 25 10 20 13 13
a
K (d-1)
half-life (d)
Methylmercury 0.0101 69 0.0068 102 0.0073 95 0.0094 74 0.0062 112 0.0065 107 0.0122 57 0.0091 77 0.0073 95 0.0127 55 0.0088 79 0.0072 97 0.01 69 0.008 87 0.01 69 0.014 50 0.00089 780 0.00099 700 0.0025 275 0.0048 163 0.0063 110 0.0022 323 0.0026 267 0.0081 86 0.022 32
[Hg] (µg g-1)
burden (µg)
duration (d)
ref
12.6 19.9 29.2
64.26 121.39 213.16
5.9 8.9 8.8 12.9 28.9 35.3
31.86 68.53 108.24 73.53 251.43 469.49
28 56 84 28 56 84 28 56 84 28 56 84 60 60 60 60 100 100 146 44 30 45 60 60 60
36
0.0097 0.0097 0.012
1.746 1.746 0.732
37 26 40 39 56 41 57 36
Chronically exposed fish.
TABLE 2. Pearson Correlation between Elimination Rate of Mercury from Fish and Weight, Water Temperature, Mercury Burden, and Concentrationa variable
FIGURE 1. Elimination rate (K) of methylmercury and inorganic mercury in relation to the duration of the experiment. Standard errors are represented by the vertical bars. overestimation of MeHg elimination rate from the small fish (1-45 g). The experiments that they performed on small fish were generally too short (
