Intercalibration of LABs in marine sediment SRM1941a and their applicationas a molecular marker in Narragansett Bay sediments

Linear alkylbenzenes (LABs) were first discharged to the environment in the early 1960s as a byproduct of linear alkylbenzenesulfonate (LAS) detergent s. Recently there has been widespread interest in their use as markers of s ewage effluent in the marine environment. However, there currently is no st andard reference material that can be widely used for method development an d/or quality control work by a laboratory wishing to do this type of analys is. An intercalibration study between two laboratories using marine sedimen t SRM1941a from the National Institute of Standards and Technology is repor ted. This standard was chosen because it is widely available, is homogeneou s, and has certified values for many organic and inorganic components. The two laboratories used different extraction, purification, and quantificatio n methods. Overall, agreement was good with an average relative percent dif ference between the laboratories of 11% for the 26 individual LAB congeners . Sediment LAB distribution in Narragansett Bay, an urban estuary that has been impacted by pollution, are reported. The concentrations of the total L ABs or Sigma LABs (sum of the 26 congeners) in surface sediments (0-2 cm) f rom throughout the bay was relatively low(median < 50 ng/g) with 8 of 41 st ations having values below the detection limit (1 ng/g). In the urban river s at the head of the bay, the Providence River, Seekonk River, and Taunton River concentrations were locally high with a few values exceeding 2000 ng/ g total LABs. The I/E (internal/ external C-12 isomers) ratio, which is a m easure of the degree of degradation, indicates that treated sources (i.e. s ewage effluents) together with local fresh sources (e.g. combined sewer ove rflows and boat cleaning detergents) are major contributors of LABs to the rivers. The observed decrease in Sigma LAB concentration with distance down bay suggests that most of the LABs, along with concomitant sewage particles and associated pollutants, are deposited within a few kilometers of their source. Sediment cores from a river and mid bay station both had a subsurfa ce maximum in Sigma LABs and then decreased to background concentrations co rresponding to the time period before LABs were first introduced into the e nvironment.