Occurrence of Polycyclic Musks in Sewage Sludge and their Behaviour in Soils and Plants. Part 2: Investigation of Polycyclic Musks in Soils and Plants (9 pp)

Abstract

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Part 2: Investigation of Polycyclic Musks in Soils and Plants Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter

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Preamble. In Part 1 of the study, screening tests were performed to investigate the occurrence of PCM in sewage sludges. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence Part 2 examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake in plants.

Goal, Scope and Background

Polycyclic Musks (PCMs) enter the terrestrial environment via the use of sewage sludge as fertilizer. After entry into soil, they can be taken up by plants or move into the groundwater body. However, until now no overall risk assessment for polycyclic musks is available. For a preliminary risk assessment further information is needed about their behaviour in the soil environment. Therefore, Part 2 of the study (Part 1, see J Soils Sediments, OnlineFirst <DOI: http://dx.doi.org/10.1065/jss2006.10.187.1>) examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake by plants.

Methods

Analytical methods for the determination of HHCB and AHTN in soil and plant samples were developed and applied. The adsorption/desorption studies were performed according to OECD guideline 106 and draft guideline 121 using three soils. Dissipation (aerobic degradation) was examined according to BBA guideline 4-1 in three soils over a test period of 37 weeks under controlled conditions. Leaching experiments in soil columns were performed using columns of 14 cm Ø and 30 cm filling height for a test period of 48 hours. Finally the uptake of PCMs by lettuce and carrots was studied in laboratory and outdoor experiments.

Results

The adsorption/desorption studies resulted in Koc values between 4200 and 7900 for HHCB and between 4800 and 13600 for AHTN showing strong sorption to the soils investigated. The dissipation of the PCMs occurred very slowly with elimination rates after 37 weeks of approx. 50% and 25% for HHCB and AHTN, respectively. The leaching experiments showed leaching rates of < 0.001% for HHCB and AHTN during a test period of 48 hours. The slight leaching is presumably due to ‘preferential flow'. The transfer factors (ratio of concentrations in the plant to concentrations in the soil ) for HHCB in lettuce and carrot leaves determined in plant uptake experiments were as low as 0.003. For HHCB in carrot roots however high transfer factors of 0.095 for a humic and 0.48 for a loamy soil were obtained. The high uptake may be caused by partitioning of the HHCB into the essential oil cells of the carrot roots.

Discussion

The polycyclic musk compounds HHCB and AHTN showed high adsorption to soil. A desorption phenomenon occurred after three desorption steps. High adsorption influences the slow degradation kinetic. Comparable investigations into the degradation behaviour show the same results, whereas other authors observed a faster degradation. We assume a dependency on microbial consortia, which can vary as a function of the substrate and adaptation of the microbial population. Leaching tests were carried out in our study, but not by other studies. The results reflect the adsorption into the soil matrix.

Conclusions

The results show that PCMs are widespread contaminants in sewage sludge and should be considered in a risk assessment as potential contaminants of sewage sludge destined for agricultural use. When applied to soil they may remain in the upper soil layers due to their high sorption, low degradability and low leaching behaviour. Uptake by some plants like carrot roots may be relevant.

Recommendations and Perspective

. This study examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake into plants. For a qualitative risk assessment more data on adsorption /desorption, and degradation in soils under different soil conditions needs to be generated. Also, further studies have to be carried out to gain a better understanding of plant uptake of PCMs, especially HHCB and AHTN.