Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations

► Limited aggregation for Au-citrate NPs at low concentrations in sea water media. ► Au-citrate NPs are not soluble in seawater after 48 h exposure. ► Gold accumulation is found under exposure of bivalve to AuNPs or chloroauric acid. ► Location of AuNPs at heterolysosomes of digestive gland cells of Ruditapes philippinarum. ► High toxicity of Au3+ dissolved species (chlororauric acid solutions).