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EP2C20F484C7N 其他数据使用手册 - Altera（阿尔特拉）

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Altera（阿尔特拉）

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changed Japanese safety limit of 100 Bq kg

−1

wet wt (about 400

Bq kg

−1

dry wt) (11). Inferences about the safety of consuming

radioactivity-contaminated seafood can be complicated due to

complexities in translating food concentration to actual dose to

humans (12), but it is important to put the anthropogenic ra-

dioactivity levels in the context of naturally occurring radioac-

tivity. Total radiocesium concentrations of post-Fukushima

PBFT were approximately thirty times less than concentrations

of naturally occurring

K in post-Fukushima PBFT and YFT

and pre-Fukushima PBFT (Table 1). Furthermore, before the

Fukushima release the dose to human consumers of ﬁsh from

137

Cs was estimated to be 0.5% of that from the α -emitting

210

(derived from the decay of

238

U, naturally occurring, ubiquitous

and relatively nonvarying in the oceans and its biota (13); not

measured here) in those same ﬁsh (12). Thus, even though 2011

PBFT showed a 10-fold increase in radiocesium concentrations,

134

Cs and

137

Cs would still likely provide low doses of radioac-

tivity relative to naturally occurring radionuclides, particularly

210

Po and

However, 2011 PBFT

134

Cs and

137

Cs concentrations were less

than they would have been in Japanese waters because of growth,

radioactive decay, and efﬂux of cesium. To estimate the

concentrations of

134

Cs and

137

Cs in 2011 PBFT at the time they

left Japanese waters, we back-calculated radiocesium concen-

trations in muscle over a range of potential trans-Paciﬁc migration

times (30–120 d) using a loss rate of assimilated Cs from ﬁsh tissue

of 1.9% day

−1

(14), growth dilution attributable to an increase in

body mass during the trans-Paciﬁc migration, and radioactive

decay (details in SI Methods). We estimated that PBFT in Japan

had 1.5–15 times higher radiocesium concentrations (30–120

d before capture, respectively) than concentrations measured at

time of capture in California (Fig. 2 and Table S1). Variations in

animal size at exposure and growth because exposure may in-

ﬂuence Cs concentrations; there was a negative trend between

animal size and

137

Cs and

134

Cs concentrations, although the

correlation was not signiﬁcant (Spearman’s ρ; Fig. S2 and SI

Methods). The Japanese Ministry of Agriculture, Forestry, and

Fisheries report post-Fukushima concentrations of

134+137

Cs in

PBFT around Japan at 61–168 Bq kg

−1

dry weight (11). Our

estimates of total radiocesium (i.e.,

134

Cs +

137

Cs) concentrations

in PBFT for 90 and 120 d before capture are 73–147 Bq kg

−1

respectively (Table S1). The similarity between back-calculated

values and those measured in Japan PBFT suggests that our

Fig. 1. (A) Map of the northern Paciﬁc ocean showing simpliﬁed movement patterns for juvenile PBFT (blue arrows) from Japan to the CCLME and juvenile

YFT (yellow arrows) in the CCLME. Kuroshio Current (gray arrow east of Japan) and CCLME (gray region west of N. America) are shown. Pie charts show mean

concentrations of

134

Cs (red) and

137

Cs (dark gray) in seawater (Bq m

) (3), and muscle tissue (Bq kg

−1

) in PBFT after Fukushima, PBFT before Fukushima, and

YFT after Fukushima. Pie charts for ﬁsh are sized to scale of total radiocesium concentrations. Black arrows show uptake (solid arrows) and efﬂux (dotted

arrows) of radiocesium in different ocean regions (arrow thickness scaled for relative efﬂux and uptake rates). (B) Simpliﬁed migration patterns of some

highly migratory species in the Paciﬁc that inhabit waters around Japan and make subsequent long distance migrations to distant ecoregions including

Kamchatka, the Aleutian Islands, North America, South America, and New Zealand. Migration patterns are shown for salmon sharks (17) (short dashed line),