Sediment Toxicity Identification Evaluation (TIE) of a coastal lagoon (Pialassa Baiona, Italy) using Microtox® system.

The Pialassa Baiona is a shallow coastal lagoon covering a surface of about 1100 ha, which lies parallel to the Northern Adriatic Sea shoreline, approximately 10 km north of the town of Ravenna. Natural and man-made changes over the time lead to existing physical features resulting in a number of different basins of less than 1 m in depth, broad and irregular in shape, separated by levees and crossed by a network of artificial channels. From the fifties, the delicate balance of life in Pialassa Baiona lagoon has been threatened by the presence of a petrochemical industrial complex, fuel oil power generation, inland intensive agriculture, as well as to the close contact with the densely populated town and coast, and human negligence. As industrial and urban development increased, so did the input of chemical contamination in the lagoon. During the last decades, various chemicals from municipal and industrial wastewaters, and agriculture runoff have been discharged into the lagoon, depending upon treatment levels, chemicals common to the time period (i.e. DDT, mercury). These sediment-borne chemicals, may, in turn, cause toxicity to aquatic organisms. As a part of an on-going study, pore water extracts were collected and evaluated with the Microtox® system using a procedure similar to the Toxicity Identification Evaluation (TIE) protocol for acute and chronic marine TIEs according to the United States EPA (US EPA/600/R-96/054). The TIE approach Phase I, namely Toxicity Characterisation, is based on the principle of sequential removal of various chemical fractions coupled with toxicity testing of the obtained fractions. When removal of a class of chemicals also removes toxicity, it is assumed that those compounds were responsible for some of the toxicity observed in the original sample. In the present study the USEPA Phase I approach was followed, and the manipulation chosen were filtration/centrifugation, metal chelation with EDTA, aeration, and passage through a C18 cartridge column. These treatments were thought to yield information on compounds responsible for toxicity. In this TIE protocol, the toxicity of the initial extract and of the various treated pore water extracts was assessed using Vibrio fischeri in the Microtox® test system, which is a rapid, low-cost toxicity test widely used in screening tests for assessing sediment toxicity. Pore water, rather than whole sediment, was chosen for evaluation because the interstitial phase has been found to be representative of the bioavailable fraction of the contaminants of concern (i.e., metals and ammonia). To this end, in tandem analysis of nitrogen ions and metals, and Microtox® test were performed on pore water samples. The addition of EDTA and the aeration step removed toxicity only in some samples. Passage through the C18 column removed toxicity in all samples, but no toxicity was found in most of the organic eluates. This may indicate either that the organic compounds responsible for toxic effects were irreversibly bound to the C18 resin, or that the organic solvent, commonly used for eluting C18 columns, was not efficient in removing all bound organic compounds. In summary, the sediment pore water toxicity is likely to be due to joint effects of confounding factors such as ammonia and sulphide, as well as metals and organic compounds.