Testing for dioxin-like potency
Dioxins are organic chlorinated compounds that are among the most dangerous known environmental pollutants. Nowadays, 210 PCDD isomers of extreme hazardousness are known. They are formed in all combustion processes in the presence of chlorine and organic carbons (from a combustion temperature of 300-900°C). Dioxins have gained particular importance in the past due to the chemical accident in Seveso (1976), in which the most toxic dioxin 2,3,7,8 tetrachloro-dibenzo-p-dioxin (TCDD) was released into the environment, and due to the use of dioxin-contaminated herbicides (Agent Orange) in the Vietnam War (1961-1971). Nowadays, these substances are now regulated by prohibition orders. However, due to the increased release in the past and the very long half-life of dioxins, they remain present in our ecosystems today as contaminated sites. Due to flood disasters and heavy rain events, they can be remobilized and re-introduced into our environment and/or taken up by organisms.
Within the Bad Waldsee project the dioxin-like potency in different sediment layers of the city lake will be investigated by means of a bioassay for different annual periods. To measure the dioxin load of an environmental sample, the biomarker "EROD" (ethoxyresorufin-O-deethylase) is usually used. EROD is a liver enzyme that is produced by organisms in direct response to contact with dioxin-like substances in order to eliminate them from the body. The enzyme, which belongs to the CYP1A enzyme family, can convert the substance ethoxy resorufin to the fluorescent dye resorufin. Thus, in biological test systems such as the micro-EROD assay, after exposure of a cell culture to the environmental sample, the fluorescence intensity can be directly related to the dioxin-like load of the tested sample. Thus, in summary, dioxin-like potency can be measured within sediments. A proof-of-concept study conducted in 2018 by Hollert et al. has already provided preliminary findings from lake sediments in the Stadtsee (Fig.3). This examined dioxin-like efficacy within sediments for the modern period (likely older than the 18th century AD), the High Middle Ages (10th to 12th centuries AD), and the Iron Age (ca. 1050 BC to 1 BC). Here, the results show the Bioanalytical Equivalents (BEQ) related to the respective sediment depth. Bioanalytical equivalents (BEQs) of mixtures and environmental samples are commonly used to reflect the potential threat of contaminants in the environment and can be determined by bioassays or by chemical analysis in conjunction with relative potencies (REPs).
