Extensi ve MeHg bi oaccumul ation li terature revi ew and meta-analysi s • MeHg bioconcentration factors atfood web base predi ctpreyfish MeHg. • DOC and trophic status influence MeHg bi oconcentration factors. • MeHg concentration in water column does notpredictMeHg in bi ota. • Conceptuali zation ofa MeHg BCF el evatorleading to a BMF stai rcase G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Editor:Yol anda Picó Methylmercury (MeHg) transferfrom waterinto the base

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... e food web (bioconcentrati on) and subsequent biomagnification in the aquatic food web leads to most of the MeHg in fish. But how important is bioconcentration compared to biomagnification in predicting MeHg in fish? To answer this question we reviewed articles in which MeHg concentrations in water,plankton (seston and/or zooplankton),as wellas fish (planktivorous and smal lomnivorous fish) were reported.This yielded 32 journalarticles with data from 59 aquatic ecosystems at22 sites around the world.Al though there are many case studies ofparticul araquatic habi tatsand specificgeographi careasthathave examined MeHg bioconcentration and bi omagni fication,we performed a meta-anal ysisofsuch studies.AqueousMeHg wasnota si gnificantpredictorofMeHg in fish,butMeHg in seston i. e. ,the base of the aquatic food web,predicted 63% of the variability in fish MeHg.The MeHg bi oconcentration factors(i . e. ,transferofMeHg from waterto seston;BCF w-s )vari ed from 3 to 7 ordersofmagnitude across sites and correlated significantly with MeHg in fish.The MeHg biomagnification factors from zooplankton to fish varied much less (logBMF z-f ,0. 75 ± 0. 31),and did notsignificantly correlate with fish MeHg, suggesting thatzooplanktivory is notas importantas bioconcentration in the biomagnification offish MeHg acrossthe range ofecosystemsrepresented in ourmeta-anal ysis.Partialleastsquare (PLS)and li nearregression anal ysesidentified severalenvi ronmentalfactorsassociated wi th increased BCF,incl udi ng low dissolved organi c carbon,low pH,and oligotrophy.Ourstudy reveal s the wi despread importance ofMeHg bioconcentration into the base ofthe aquati c food web forMeHg athi ghertrophic levelsin aquati c food webs,aswel las the majorinfluences on the variabi li ty in thi s bi oconcentration.