Suwanna Panutrakul

A novel arsenic containing riboside (arsenosugar) in three species of gastropod

Abstract Arsenic compounds in three marine gastropods ( Thais bitubercularis, Thais distinguenda, Morula musiva ) from Phuket, Thailand were examined by HPLC using ICP-MS as an arsenic specific detector. Aqueous methanol treatment of the freeze-dried samples (initially 112–339 μg As g −1 dry mass) extracted >96% of the total arsenic. HPLC-ICP-MS of the extracts demonstrated the presence of arsenobetaine (93–95% of total extractable arsenic), arsenocholine (3.1–4.6%), tetramethylarsonium ion (0.21–2.2%), two unknown arsenic compounds (each approx. 0.1%), and an unresolved mixture of arsenic compounds (∼1%). One of the unknowns was identified as a new natural product, the arsenosugar 2′,3′-dihydroxypropyl 5-deoxy-5-trimethylarsonioriboside, by co-chromatography with synthetic material. The presence of these arsenic compounds in the gastropods is consistent with the hypothesis that trimethylated arsenosugars are transformed into arsenobetaine via arsenocholine within animals.

BEHAVIOUR OF HEAVY METALS IN A MUD FLAT OF THE SCHELDT ESTUARY, BELGIUM

Abstract The Ballasplaat intertidal mud flat in the Scheldt estuary has been polluted by Cd and Pb and also high amounts of organic matter as a result of suspended matter deposition. The degree of pollution is, however, not uniform over the mud flat due to varying physicochemical conditions (essentially variable redox profiles). Measurements of the redox profile, and the metal concentrations in the pore water, the total sediment and the fraction

Geochemistry of mercury in an intertidal flat of the Scheldt estuary

Sediments were sampled on the ‘Groot Buitenschoor’, an intertidal flat located at about 60 km from the Scheldts river mouth. Hg concentrations ranged from 30 to 1756 ng g−1. The concentrations were strongly correlated with fine grain fraction, organic matter content and sulphide concentrations. Incubation experiments were performed in order to determine the potential methylation rate of Hg as well as biotic and abiotic factors influencing this transformation. About 1 to 2% of the added inorganic Hg is converted into methylmercury. This conversion rate points to the same equilibrium ratio as was observed in natural sediments, indicating an equilibrium between methylation and demethylation reactions in the sediments. Incubation of a sterilised sediment sample significantly decreased the methylation rate, but the methylmercury concentrations observed are still ten times higher than the natural (unspiked) sediment. This result could be due to a chemical (non-enzymatic) methylation of mercury. Sulphate reducing bacteria are the main species responsible for the methylation of Hg at this site. Addition of Na2MoO4, a specific inhibitor of sulphate reducing bacteria, decreased the methylation rate to the abiotic level (sterilised sediment). High sulphate reduction rates, however, lead to lower methylation rates. Increased formation of sulphides due to microbial sulphate reduction leads to enhanced HgS formation and this reaction competes with the methylation process. HgS is in fact the major product formed by the reaction of sulphate reducing bacteria with Hg species. About 50% of the Hg spiked to the sediments is transformed into HgS during the incubation experiments, and that compound is practically unavailable for methylation in contrast to other bound forms of Hg.

Geochemical processes in muddy and sandy tidal flat sediments

Different approaches, such as element analyses of the bulk sediment and of the fine sediment fraction (<63 μm), sequential extraction techniques, correlation coefficient, and enrichment factor calculations, clearly demonstrate the differences in geochemical behavior of a muddy and a sandy sediment on the same tidal flat in the Scheldt estuary (Belgium). The geochemical processes in combination with the relatively large transport mobility of dissolved compounds due to the tidal action in the sediment, created compound specific vertical distribution profiles.

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (So), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol−1) than at station A (Ea=110 kJ mol−1). The maximum SRR values observed equalled 14 μmol cm−3 d−1 at station B and 1 μmol cm−3 d−1 at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and So were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m−2 yr−1, and at station A of the order of 12 mol m−2 yr−1. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.

Microbial activity in sandy and muddy estuarine sediments

Striking differences were observed in the use of the electron acceptors involved in the degradation of organic matter by heterotrophic bacterial activity between a muddy and a sandy sediment on the same tidal flat of the Scheldt estuary. These bio-reduction reactions could have a quite different effect on the cycling of trace metals in the sediment as suggested by the results of the mobilization experiments. Trace metal speciation can be described as a function of the redox potential, in view of the fact that the latter is related to the heterotrophic bacterial activity.

THE PRESENCE OF THE PACIFIC WHITELEG SHRIMP (LITOPENAEUS VANNAMEI, BOONE, 1931) IN THE WILD IN THAILAND

Abstract Pacific whiteleg shrimp (Litopenaeus vannamei, Boone, 1931) was first introduced to Thailand for aquaculture in the late 1990s as an alternative to a native shrimp species, black tiger prawn (Penaeus monodon, Fabricius, 1798). We documented the presence of L. vannamei in the Bangpakong river system, an important watershed in eastern Thailand with a high density of shrimp farms. This paper is a part of a larger study to evaluate potential ecological consequences of introduced L. vannamei. During January–November 2005 (three sampling periods), we sampled wild marine shrimp with commercial shrimp nets (6 m wide × 5 m deep × 25 m long with 2.5 cm mesh) at four sites within the Bangpakong estuary. Results indicated that L. vannamei were present at least once at all sampling sites during the study. Proportion of L. vannamei relative to all Penaeid shrimp per net in the Bangpakong estuary was 0.005 ± 0.0016 (January–March 2005), 0.0005 ± 0.00021 (June 2005), and 0.061 ± 0.0035 (September–November 2005). Litopenaeus vannamei were present in 30%, 16% and 100% of nets used for the three consecutive sampling periods. The mean sizes of L. vannamei captured were 22.4 ± 0.75, 25.1 ± 0.07, and 22.0 ± 0.29 mm postorbital carapace length (PO-CL) and 85.6 ± 2.66, 105.5 ± 6.13, and 85.8 ± 1.04 mm body length. The CL and body sizes were significantly larger in samples collected in June 2005 than the two other periods. Increasing frequencies of occurrence of L. vannamei in the Bangpakong estuary call for the determination of sources (escapes versus a self-sustaining population) and mitigation.

HEAVY METALS IN WILD BANANA PRAWN (FENNEROPENAEUS MERGUIENSIS DE MAN, 1888) FROM CHANTABURI AND TRAT PROVINCES, THAILAND

Abstract Concentrations of the heavy metals cadmium (Cd), mercury (Hg), nickel (Ni), lead (Pb), chromium (Cr), copper (Cu) and zinc (Zn) in adult banana prawns (Fenneropenaeus merguiensis de Man, 1888) were determined. Banana prawn samples were collected from two provinces of Thailand (Ampur LamSing, Chantaburi, and Ban Huanumkao, Trat) by gill net. Twenty five prawns from each province were randomly chosen from the catch and each prawn sample was divided into two parts: cephalothorax and abdominal muscle. Both parts were digested with concentrated nitric acid and hydrogen peroxide under pressure in a microwave digester. Hg levels were determined using a Cold Vapor Atomic Fluorescence Spectrometer. Cd, Cu, Cr, Ni, Pb, and Zn concentrations were determined using Atomic Absorption Spectrophotometer. Trace concentrations of Cd, Cu, Cr, Ni, Pb, and Zn in cephalothorax of banana prawns from both provinces were significantly higher (P < 0.05) than in muscle, with no significant difference observed for Hg. Concentrations of Hg, Cu, Zn, and Cd in banana prawns from Chantaburi province were significantly higher (P < 0.05) than those from Trat province. There was no significant difference observed between the contents of Pb, Ni, and Cr in banana prawns caught from the two provinces. Heavy metal content in banana prawn, especially in cephalothorax tissue, may be a good indicator (sentinel organism) of heavy metal contamination in the coastal environment. Mean concentrations of all heavy metals in abdominal muscle (edible part) were within the safety limits for human consumption. However, Cd and Cu concentrations in some of the cephalothorax samples from Chantaburi province were higher than the safety limits for human consumption. This suggests that a close monitoring program is needed to ensure the safety of F. merguiensis as a food source.

SPECIES AND DISTRIBUTION OF PENAEOID SHRIMPS IN THAILAND

Abstract Species and distribution of Penaeoid shrimps in Thailand were studied in specimens of shrimp collected from fish markets and fishing ports of 23 provinces along the Gulf of Thailand and the Andaman Sea coast. Identification of species was based on the morphological characters of rostrum, carapace, branchiae, antennule, antenna, third maxilliped, pereiopods, pleopods, abdomen, telson, petasma, thelycum, and the colored pattern of the whole body based on keys and diagnoses available from the current literature. A total of 50 species from 13 genera and 3 families of Penaeoidea were identified in coastal provinces of the Gulf of Thailand and the Andaman Sea. Additional research is needed to more clearly define the distribution of shrimp species in the Gulf of Thailand and the Andaman Sea coasts.