Results & Discussion 1：the CsMPs in 
    aquatic insects
     •                                        137
       Relationships between                      Cs activity concentration and weight  of                                               • All samples were collected at 
       individuals.                                                                                                                         OD1.
                             Caddisfly larvae                                            Dragonfly larvae
                              (Stenopsyche marmorata)                                         (Protohermes grandis)                      • Autoradiography found the 
           )                                                                                                                                CsMPs from three outliers (A-C) 
           y
           r              C                                                                                                                 in caddisfly larvae which 
           d
           -
           g                                                                                                                                showed an order of magnitude 
           k
           /
           q                                            N=47                                                                                higher 137Cs activity 
           B                                        A
           (
                                                                                                                                            concentration.
           n                                        Removing CsMPs 
           o                                                         B
           i                             CsMPs from sample 
           t
                                                               137                                                                          137
           a                                        decreased    Cs                                                                      •     Cs concentration of both 
           r                                        concentration.                                                     N=45
           t                                                                                                                                aquatic insects decreased with 
           n
           e                                                                                                                                larger body size (P < 0.001).
           c
           n                                                                                                                                 
           o                                                                                                                                This may be caused by smaller ratio 
           c
            
           y                                                                                                                                of the weight of the digestive tract 
           t
           i                                                                                                                                content to total body weight in larger 
           v
           i
           t                                                                                                                                individuals ( and higher 
           c
           a                                                                                                                                concentration of 137Cs than the rest 
            
           s                                                                                                                                of the body).
           C
          7
          3
          1
                                                                                                                                         • Smaller variability of 137Cs 
                           Weight of individuals (mg-dry)                               Weight of individuals (mg-dry)                      concentrations in dragonfly 
                                                                                                                                            larvae.
                  diet : net-spinning collector feeder 
                  that feed on drifting organic matters                          diet : carnivorous predators of other                   • Caddisfly larvae feed on drifting 
                  including diatoms, periphyton and                              aquatic insects.                                           fine particulate organic matter 
                  detritus.                                                                                                                 captured in the nets, so they 
                                                                                                                                            are more likely to take up 
                                                                                                                                            CsMPs with diet particulates 
                                                                                                                                            into their digestive tract than 
                                                                                                                                            dragonfly larvae.
    Results & Discussion 2：The frequency of CsMPs in insects and their 
    diet
        • Radioparticles with more than 0.1 Bq of 137Cs using autoradiography were considered as 
               CsMPs. 
        • CsMPs were also found from periphyton, CPOM and SS samples which can be source of 
      Information of the found CsMPs
               caddisfly diet.                                                                                                                                                                                                                   Frequenc
                                                                                                                                                                                                                  137                                  y of 
                                                                                                                  137                                               137                                                Cs 
                                                                                         Number                        Cs fraction                                       Cs                            concentration                                CsMPs                   Particle 
              Sample                                     ID           Site              of CsMPs                       of CsMPs                          concentration                                without CsMPs                                   (per                       size                                                         134                   137
                                                                                                                             (：)                     with CsMPs (Bq/g)                                                                                                          (μm)                                                                Cs  /                 C  ratio  of 
                                                                                                                                                                                                                 (Bq/g)                             gram)                                                                                 CsMPs
                                                          A               J1                     1                         96.4                              14.6 ± 0.2                                   1.07 ± 0.03                                5.2 –                     FPOM                                                                                                                           EDS 
              Caddisfly                                   B               J1                     1                         95.4                               7.7 ± 0.1                                   0.39 ± 0.03                                15.6                      0.45–                                                                                                                          spectra
              larvae                                      C               J1                     1                         96.8                              39.8 ± 0.8                                   1.22 ± 0.07                                  (gut                    1000                                                                                                                           of CsMPs
                                                                                                                                                                                                                                                   content)
                                                          D            St.2                      7                           3.1                             28.2 ± 0.3                                           27.3                                                            All 
              Periphyton                                  E               J3                     1                         16.7                              11.2 ± 0.1                                            9.3                              0.48                     particle 
                                                                                                                                                                                                                                                                                sizes                                                                                                   The CsMPs were
                                                          F            St.4                    10                            0.6                             12.1 ± 0.2                                           12.0                                                                                                                                                         type-A particles emitted 
                                                          G            St.4                      0                             0                             17.0 ± 0.3                                               –                                                                                                                                                                              from
                                                          H            St.3                      0                             0                              8.5 ± 0.2                                               –                                                                                                                                                        Unit２or 3 of the FDNPP.
              CPOM                                         I           St.2                      9                           2.2                             12.9 ± 0.2                                           12.7                              0.17                     > 1000
                                                                                                                                                                                                                                                                                                                Caddisfly larvae                                       Periphyton                                    Periphyton
                                                           J           St.1                      2                           7.8                             11.3 ± 0.3                                           10.4                                                                                                  3.67 Bq                                           4.84 Bq                                       3.39 Bq
                                                          K            St.1                      0                             0                              9.7 ± 0.2                                               –
                                                          L            St.1’                     1                         58.9                              279  ± 3.9                                         114.5
              SS                                          M St.1’                                1                           2.2                              580 ± 3.5                                         567.3                               5.94                      > 0.45
                                                          N            St.1’                     1                           1.9                              248 ± 7.9                                         243.2
                 137                                                                            137                                          137
             *       Cs fraction of CsMPs = ( CsMPs total                                           Cs ) / ( sample total                         Cs) 
             * Frequency of CsMPs = Number of CsMPs / sample weight ( weight include samples without CsMPs ).
                                                                                                                                                                                                                                                                                                                                 CPOM                                                                                           SS
           •     137Cs fraction of CsMPs is high in caddisfly larvae. When the total 137Cs radioactivity in samples are small,                                                                                                                                                                                                 3.44 Bq                                                                                     3.44 Bq
                 CsMPs incorporation cause large variation of 137Cs concentrations between samples.
           •     Frequency of CsMPs was high and comparable for the gut content of caddisfly larvae and their diet (SS).
                 The Particle size of CsMPs were similar to that of the caddisfly diet, which allows easy 
                 uptake of CsMPs.
           •                  137                                                                                                                                                                               137
                 The                Cs bioavairability in CsMPs may be low because dissolution of                                                                                                                     Cs can be very small in a                                                        SEM images of 
                 few days                                                                                                                                                                                                                                                                              CsMPs
                 before CsMPs is expelled from the digestive tract.