Water samples (n = 107) taken from nine English freshwater lakes from a mix of urban, rural, and remote locations on 12 occasions between August 2008 and February 2012, and archived suspended sediment samples (n = 39) collected over the period 1980-2012 at the mouth of the Niagara River in Lake Ontario were analysed to assess the temporal trends in contamination by the three main hexabromocyclododecane (HBCD) diastereomers (α-, β-, and γ-HBCD). HBCDs (45 to 890 pg L, n = 107) were generally equally distributed between the operationally defined freely dissolved and particulate phases in English lake water. Concentrations of HBCDs declined over the sampling period with half-lives of 5.1 years in English water, with a significantly decreasing trend also observed for Niagara River suspended sediments (NRSSs). With respect to seasonal trends, significantly higher concentrations were found in colder compared to warmer periods at 5 out of 9 English lakes, while NRSSs in this study revealed no statistically significant seasonal trends. The maximum HBCD concentration in NRSSs was about 3 orders of magnitude lower than those detected in English lake water, which is plausible given the greater per capita use of HBCD in Europe than North America. While γ-HBCD was consistently dominant (35-86%; mean = 56%) in English lake water samples, and dominated in NRSSs collected prior to 2002 inclusive (13-100%, mean = 73%), the abundance of γ-HBCD was significantly lower (3.5-37%; mean = 23%) in NRSSs from 2003 onwards.
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