There is little information available on the distributions of micro-organic
contaminants in river bed-sediments below a depth of 5 cm. The aim of this
study is to determine the concentrations and distributions of contaminants
in river bed-sediments up to 1 m depth and to make an assessment of the re
sults. The approach taken was to collect five cores from each of two lowlan
d rivers in southern England, the first a rural river and the second a domi
nantly urban catchment. The cores were analysed for micro-organic compounds
and sediment/sediment porewater characteristics. Compounds detected were p
olyaromatic hydrocarbons (naphthalene, fluoranthene and pyrene), pesticides
(carbaryl, linuron, fenpropimorph, the synthetic pyrethroids, and prometry
n), and non-ionic surfactant residue (nonylphenol). A particularly importan
t finding was that some micro-organic contaminants penetrated to depths of
1 m, and in one of the rivers they were detected in undisturbed Eocene subs
trata. The more hydrophobic contaminants showed a clear depth distribution
with higher concentrations towards the top of the cores. The less hydrophob
ic contaminants demonstrated no systematic trend suggesting they had become
soluble in porewaters and subsequently travelled within the cores. Partiti
on between the porewater and sediment appeared to be controlling the distri
bution of the compounds with depth. (C) 2000 Elsevier Science B.V. All righ
ts reserved.