The stability of butyltin compounds in a dredged heavily-contaminated sediment

doi:10.1016/j.chemosphere.2007.01.074

Chemosphere

Volume 68, Issue 6, June 2007, Pages 1114-1119

https://doi.org/10.1016/j.chemosphere.2007.01.074 Get rights and content

Abstract

A treatment process for marine sediment heavily contaminated with tributyltin (TBT) was designed that included dehydrating, sunlight drying and dumping processes. The time course in butyltin (BTs) compounds, TBT, dibutyltin (DBT) and monobutyltin concentrations were investigated in the sediment treated under various conditions (light (UV, sunlight and light exclusion), moisture (air-drying and water saturation) and wetting and drying cycles). Significant changes in all the BT compound concentrations with time were not found regardless of the sediment conditions for light and moisture. The results indicated the high stabilities of TBT and DBT in the sediments versus light and moisture condition changes, probably taking place in the treatment process. It is also estimated that the BTs in the sediment are resistant to photo-degradation and biochemical degradation and their half lives are relatively long. In contrast, the decreases in the TBT and DBT were observed during the wetting and drying cycle treatment for the water saturated sediment both during exposure to sunlight and under a dark condition. This result suggested the hypothesis that the TBT degradation could be accelerated by the high microbial activity induced by the moisture changing treatments.

Introduction

Organotin (OTs) compounds, including butyltin (BTs) compounds and phenyltin compounds, have been widely used as an antifouling agent in aquatic environments since the early 1960s. BTs are represented by two compounds, tributyltin oxide (TBTO) and tributyltin chloride (TBTCl). It is well-known that the degradation of tributyltin (TBT) in the environment and in vivo is defined as sequential removal of the butyl groups from the tin (Sn) atom (Navio et al., 1993),Bu₃SnX(TBT) → Bu₂SnX₂(DBT) → BuSnX₃(MBT) → SnX₄where X represents halogen atoms. The removal of the butyl groups is mainly caused by three processes: ultraviolet irradiation, biological cleavage and chemical cleavage (Hoch, 2001). The highest toxicity of the BTs is shown by the TBT species (Maguire, 1987).

Since 1982, many governments of developed countries, i.e., France, USA, UK, Canada, Austria, Sweden and Switzerland, have regulated the use of TBT-containing paints for vessels <25 m in length. Also in Japan, the restriction on TBT use in the anti-fouling coatings of boats and aquaculture nets was implemented in 1990. However, in most countries exceptions to the rules exist for vessels with an overall length >25 m like oceanliners and military ships. In spite of the banning or regulation of using of TBT in some countries, the contamination continues in the aquatic environment, and environmental concentrations remain high enough to warrant continued concern (Hoch, 2001). Especially, in marine sediments, many BT compounds still remain, possibly continuing to affect the marine ecosystem. As a countermeasure of the marine pollution, the dredging and land treatment of the contaminated sediments will be required in the future.

Our research group has investigated and manufactured a treatment process for dredging TBT-contaminated sediments. This process involves dredging of the sediments, separation of the liquid and solid of the sediment slurry, removal of the BT compounds in the separated water, and land-dumping of the separated solid from the sediment. The removal treatment of BTs from the separated water involves the use of a coagulant called PSI-100 and then a series of infiltrations consisting of a fiber sheet sand and activated carbon. The wastewater treatment process succeeded in lowering the TBT concentration in the separated water from 9 μg l⁻¹ to 2 ng l⁻¹, which is less than the TBT emission permissible concentration of 7 ng l⁻¹ (Ito et al. personal communication). After removal of the liquid portion, the process is designed to dry the solid portion of the sediments in sunlight, then dump it in a landfill. Through the process, the sediment solid should have undergone various environmental influences such as drying and sunlight exposure. Because the degradation of TBT in the environment fluctuates under various conditions, the evaluation of the environmental influence on the degradation of TBT is essential in elucidating the behavior and fate of the compounds in the sediments.

The purpose of the present study is to understand the effects of the treatment process including dehydrating, sunlight drying, and dumping, on the behavior of the BT compounds in the sediment heavily contaminated with TBT.

Section snippets

Sediment sample

A sediment sample was collected in 2004 in the coastal area near a shipyard located in Nagasaki Prefecture, Japan. The sediment samples were incubated in Petri dishes under the various conditions described below. The temperature and humidity were constant at 20 ± 1 °C and 70 ± 1%, respectively. As the treatment process for the contaminated sediments was designed, including dehydrating, sunlight drying and dumping processes, the sediment sample were treated using combinations of three conditions

Properties of the sediment

The carbon content of the sediment sample was 7.3% on the dry weight basis. After digestion with conc. HCl, the heavy metal elements of the sample, including Sn, were determined by ICP-MS (Agilent 7500C) at the Center of Advanced Instrumental Analysis, Kyushu University. The total Sn concentration in the sample was 105 μg g⁻¹ (dry weight basis). The sediment sample contained other metals; i.e., 43.7 μg g⁻¹ of Cr, 2448 μg g⁻¹ of Cu, 1667 μg g⁻¹ of Zn, 13.4 μg g⁻¹ of As and 665 μg g⁻¹ of Pb.

The TBT, DBT and

Conclusion

The significant degradation of all BTs with time were only slightly verified in the sediments even by light and drying treatments. Thus, the results suggested that the BT compounds in the sediment discharged from the TBT contaminated sediment treatment plant would be very stable to photo- and bio-degradations during a relatively short time. Their half lives would also be so long as to reach several years. The decreases in the TBT and DBT were observed with the changing moisture treatments for

Acknowledgements

The authors thank Assistant Prof. Y. Shimazaki, Kyushu University, for advising on this study. This research was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (subject number 16310060).

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The stability of butyltin compounds in a dredged heavily-contaminated sediment

Abstract

Introduction

Section snippets

Sediment sample

Properties of the sediment

Conclusion

Acknowledgements

Chemosphere

Environ. Pollut.

Environ. Pollut.

Appl. Geochem.

Chemosphere

J. Photochem. Photobiol. A: Chem.

Environ. Pollut.

Environ. Pollut.

Environ. Pollut.

Soil Biol. Biochem.

Kandokouka (Air drying effect on ammonification)

The effect of soil drying on humus decomposition and nitrogen availability

Plant Soil

Environmental tributyltin research: past, present, future

Environ. Technol.

Depositional profiles and relationships between organotin compounds in freshwater and estuarine sediment cores

Environ. Monit. Assess.

A proposed mechanism for the pulse in carbon dioxide production commonly observed following the rapid rewetting of a dry soil

Soil Sci. Soc. Am. J.