Phthalic acid diesters comprise a large group of organic compounds that are used to manufacture a variety of products all over the world, and this has raised concerns about the fate of these compounds in the environment. The diester-containing products often end up in landfills, where they are degraded by various micro-organisms, which gives rise to transient intermediates such as phthalic acid monoesters and ortho-phthalic acid. These degradation products escape detection when applying the analytical protocols used to investigate the well-elucidated diesters, hence other methods are needed.

In the present work, the temporal pattern of degradation was scrutinised by studying leachates from both laboratory-scale Iandfill simulation reactors and newly established fullscale landfill cells. Leachate samples from a transect downstream of a landfill were also examined to highlight possible groundwater contamination from unlined landfills. In addition, extraction techniques were developed for simultaneous detection of diesters, monoesters of o-phthalic acid, and o-phthalic acid itself.

The degradation products of phthalate diesters (i.e. the monoesters and phthalic acid) were found in the landfill leachates, which demonstrates proves that phthalic acid diesters are degraded/transformed in situ in landfills. The monoesters and phthalic acid may accumulate in leachates during certain parts of landfill degradation development, for example, during establishment of the methanogenic micro-flora. The phthalates leached from landfills are potential groundwater contaminants, whereas breakdown of the diesters and monoesters was observed in the studied Iandfill plume. The monoesters and phthalic acid could be detected by proper acidification of the samples and derivatization of the extracts, followed by gas chromatography and mass spectrometry. Acute toxicity tests showed that the monoesters were generally less toxic than the corresponding diesters, and that phthalic acid was the least toxic. These results suggest that degradation of the diesters to monoesters and phthalic acidwill reduce the risk for acute toxic effects on the environment.