Intercalibration of LABs in Marine Sediment SRM1941a and Their Application as a Molecular Marker in Narragansett Bay Sediments

Abstract

Linear alkylbenzenes (LABs) were first discharged to the environment in the early 1960s as a byproduct of linear alkylbenzenesulfonate (LAS) detergents. Recently there has been widespread interest in their use as markers of sewage effluent in the marine environment. However, there currently is no standard reference material that can be widely used for method development and/or quality control work by a laboratory wishing to do this type of analysis. An intercalibration study between two laboratories using marine sediment SRM1941a from the National Institute of Standards and Technology is reported. This standard was chosen because it is widely available, is homogeneous, and has certified values for many organic and inorganic components. The two laboratories used different extraction, purification, and quantification methods. Overall, agreement was good with an average relative percent difference 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 LABs or ΣLABs (sum of the 26 congeners) in surface sediments (0−2 cm) from throughout the bay was relatively low (median < 50 ng/g) with 8 of 41 stations having values below the detection limit (1 ng/g). In the urban rivers 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 measure of the degree of degradation, indicates that treated sources (i.e. sewage effluents) together with local fresh sources (e.g. combined sewer overflows and boat cleaning detergents) are major contributors of LABs to the rivers. The observed decrease in ΣLAB concentration with distance downbay 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 subsurface maximum in ΣLABs and then decreased to background concentrations corresponding to the time period before LABs were first introduced into the environment.