Polychlorinated n-alkanes (PCAs), also known as chlorinated paraffins, are a class of high molecular weight organochlorines (OCs) used as high pressure lubricants, flame retardants and a number of other industrial applications. Reviews of information available on PCAs have concluded that there is a lack of data to assess their fate and effects in the environment. This work has examined the dietary accumulation, sediment bioavailability and toxicity of a range of PCAs which vary in carbon chain length and chlorine content. PCAs (C$\sb{10}$-, C$\sb{11}$-, C$\sb{12}$-, C$\sb{14}$- and C$\sb{16}$) were accumulated from food by juvenile rainbow trout (Oncorhynchus mykiss). PCA half lives (t$\sb{1/2}$, range 7.1-87 d) and biomagnification factors (BMFs) (0.14-2.2) increased with carbon chain length and chlorine content. PCAs were biotransformed but the biotransformation rate was inversely related to chlorine content. Highly chlorinated ($>$60% Cl) short chain (C$\sb{10{-}13}$) and medium and lower chlorinated ($<$60% Cl) medium chain (Cl$\sb{14{-}18}$) PCAs appear to have the greatest potential for bioaccumulation. Dietary accumulation experiments using juvenile rainbow trout and 23 hydrophobic recalcitrant OCs revealed curvilinear relationships between K, and assimilation efficiency, t$\sb{1/2}$, a d BMF, peaking at a log K$\sb{\rm ow}$ of approximately 7.0. Decreasing t$\sb{1/2}$ above log K, of 7 was unexpected and may have been due to an insufficient accumulation period (30 d). C$\sb{12}$ (56 and 69% Cl)- and C$\sb{16}$ (35 and 69% Cl)-PCAs were accumulated from sediments by oligochaetes (Lumbriculus variegatus) suggesting that sediment-sorbed PCAs should be available to benthic biota. Half lives of the C$\sb{12}$-PCAs (11-13 d) were lower than C$\sb{16}$-PCAs (24-43 d). Biota sediment accumulation factors (BSAF) were $>$1 for the C$\sb{16}$-PCAs and the lower chlorinated C$\sb{16}$-PCA (35% Cl), but $<$1 for the high chlorinated C$\sb{16}$-PCA (69% Cl). Toxicity tests on 6 PCAs of a single carbon chain length and known chlorine content using Japanese medaka (Oryzias latipes) embryos and juvenile rainbow trout suggested that the toxic mode-of-action is narcosis. Some evidence of histopathological lesions in the liver were observed in rainbow trout exposed to high dietary concentrations of PCAs, suggesting that PCA may cause sub-lethal effects in fish at very high exposure concentrations.