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Glass fibre predicts uptake in earthworms

June 24, 2003

Dutch researchers have discovered that glass fibres absorb the same types and quantities of toxic substances from damp soils as earthworms, which form the basis of the current methods soil researchers use for toxicity analyses.

The Institute for Inland Water Management and Waste Water Treatment (Dutch acronym: RIZA) now uses glass fibres to measure water pollution and sediment pollution. Toxicologists carefully shake soil samples with water in a machine. This releases the available pollutants into the water surrounding the soil particles. The glass fibres then absorb the pollutants from the water. After this gas chromatography is used to determine which toxic substances are present in the glass fibre and were therefore present in the soil.

The method is much faster than the technique using worms. The worms need to crawl through the soil sample in the laboratory for several days. Then the researchers have to freeze the worms, dry them and then grind them to extract the toxic substances.

Toxicologist Leon van der Wal tested the glass fibre method on soil from Rotterdam that had been sprayed with dredged silt during the 1970s. The experiments revealed that worms only came into contact with ten percent of the toxic substances present in soil. This is because over the course of time many of the toxic substances have become bound to soil particles. A determination of the total amount of toxic substances present in soil would therefore have overestimated the soil danger by a factor of ten. The glass fibre method only gave a small overestimation of the toxic substances available.

Contrary to what was previously thought, the comparison of the two methods revealed that, based on total extraction procedure, the uptake of strongly hydrophobic substances by worms is underestimated whereas the uptake of less hydrophobic compounds is overestimated. As the fibre method is based on porewater concentrations, it gives a better prediction of expected concentrations than methods using earthworms.

NWO (Netherlands Organization for Scientific Research)