VARIABILITY OF ORGANIC CONTAMINANTS IN INTER-TIDAL SANDFLAT SEDIMENTSFROM MANUKAU HARBOR, NEW-ZEALAND

Surficial sediments from five stations on inter-tidal sandflats within Manukau Harbour, New Zealand were sampled using a systematic sampling design to give three representative bulked replicates per station. Pa rticle size analysis showed the stations to be similar, with poorly so rted fine to medium sand and mud contents of 21-26%. Sediment readily oxidizable carbon contents were low (0.22-0.73%). These parameters sho wed similar variability (CVs of 11-50%), both within and between stati ons, confirming their visual similarity. Organochlorine insecticides, PCBs (23 congeners) and polynuclear hydrocarbons (PAHs, 10 fluorescent compounds) were extracted from the sediments and determined to detect ion limits of 0.02-0.05 ng/g. An extraction procedure using a ternary solvent system (acetone/hexane/water) gave equivalent results to a sta ndard method but was more rapid, used less solvent, and gave lower bla nks. Levels of chlorinated organics were low. Highest levels for all c ontaminants occurred at one station (total PCBs 1.6 ng/g, DDT + metabo lites 18 ng/g, dieldrin 0.38 ng/g lindane 0.34 ng/g, cis- + trans-chlo rdane 0.38 ng/g, total PAHs 3,740 ng/g). PAH levels were substantially lower at other stations (40-90 ng/g). Differences for other contamina nts were not great, although there was a significant gradient of chlor dane concentration between the stations. Variability in concentrations of contaminants was large both within and between stations (CVs of 2- 126%). Normalizing the concentrations to organic carbon did not marked ly alter the above trends, but demonstrated significant chlordane and PCB gradients, and increased the variability within many of the statio ns. The results were interpreted as indicating multiple contaminant so urces, with major contributions from the treated sewage out-fall and a more heavily contaminated industrialised inlet at the head of the har bour. The contaminants were not strongly associated with any particula r sediment characteristic, with only PCBs strongly correlated with car bon levels.