Sequential extraction analysis of heavy metals using a chelating agent (NTA) to counteract resorption

The geochemical partitioning of Pb, Ni and Zn in contaminated quartz-rich sediment and soil samples was characterized by sequential extraction analysis in the presence and absence of nitrilotriacetic acid (NTA). With NTA, levels of metals recovered are higher in the earlier steps and lower in the later steps of the procedure. This suggests that post-extraction resorption is effectively counteracted by chelation, thereby improving the accuracy of the method. An NTA concentration of 200 mg liter(-1) appears to be sufficient for counteracting resorption without causing significant dissolution of non-targeted phases in the samples studied. However, experiments using reference materials spiked with solutions containing Pb, Ni, Cu and Zn suggest that resorption will remain a problem when large amounts of strong sorbents such as organic matter are present. The results also show that although post-extraction resorption does occur in the absence of NTA, the magnitude of resorption is small (<20 to 30% of the summed total of metal present in the sample) in quartz-rich sediments.     

Nitrilotriacetate- and citric acid-assisted phytoextraction of cadmium by Indian mustard (Brassica juncea (L.) Czernj, Brassicaceae)

In a pot experiment the effects of nitrilotriacetate (NTA) and citric acid applications on Cd extractibility from soil as well as on its uptake and accumulation by Indian mustard (Brassica juncea) were investigated. Plants were grown in a sandy soil with added CdS at four levels ranging from 50 to 200 mg Cd kg(-1) soil. After 30 days of growth, pots were amended with NTA or citric acid at 10 and 20 mmol kg(-1). Control pots were not treated with chelates. Harvest of plants was performed immediately before and one week after chelate addition. Soil water-, NH(4)NO(3)- and EDTA-extractable Cd fractions increased constantly with both increasing soil metal application and chelate concentration. Shoot dry weights did not suffer significant reductions with increasing Cd addition to the soil except for both NTA treatments in which at 200 mg Cd kg(-1) a 30% decrease in dry matter was observed. Generally, following NTA and citric acid amendments, Cd concentration in shoots increased with soil Cd level. However, due to Cd toxicity, at the highest metal application rate both NTA treatments lowered Cd concentration in the above-ground parts. Compared to the control, at 10 mmol kg(-1) citric acid did not change Cd concentration in shoots, whereas NTA-treated plants showed an about 2-fold increase. The addition of chelates at 20 mmol kg(-1) further enhanced Cd concentration in shoots up to 718 and 560 microg g(-1) dry weight in the NTA and citrate treatments, respectively.     

Influence of sodium nitrilotriacetate (NTA) and citric acid on phenolic and organic acids in Brassica juncea grown in excess of cadmium

Brassica juncea cv. 426308 was grown in soils containing 150 mg Cd(2+)kg(-1) soil. After 38 days, the soil was amended with two rates of citric acid or NTA (10 and 20 mmol kg(-1) soil). Control soil was not amended with chelates. Plants were harvested during growth, immediately before and seven days after chelate addition. Shoot composition of organic and phenolic acids and shoot Cd(2+) concentration were determined. Cadmium concentration remained constant during the growth and increased following NTA and citric acid amendments depending on chelate type and concentration. The highest increments in Cd(2+) were measured after the addition of NTA. Compared to the control, 10 and 20 NTA-treated plants showed two- and three-fold increases, respectively. At 150 mg Cd(2+)kg(-1) soil the amount of organic and phenolic acids in the leaves of B. juncea was always higher than that detected in the control. A direct correlation between organic acid concentration and cadmium content was detected both during growth and after chelate addition. On the contrary, the amount of phenols seemed to be correlated with the metal content only in non-amended and NTA-treated plants. The 10 and 20 citric acid additions caused 45% and 90% increases in shoot phenolic acids although cadmium content rose to a smaller extent. The inhibition of citrate synthase and the entrance of phosphoenolpyruvate in shikimate pathway leading to the formation of aromatic compounds might come into play. The increase in phenylalanine ammonialyase activity following citric acid amendments suggested this metabolic response.     

Effects of low dissolved oxygen on organisms used in freshwater sediment toxicity tests

Minimum dissolved oxygen requirements are part of standard guidelines for toxicity testing of freshwater sediments with several benthic invertebrates, but the data underlying these requirements are somewhat sparse. We exposed three common test organisms to ranges of dissolved oxygen concentrations to determine their responses in 10-d exposures, relative to published guidelines for sediment toxicity tests. The oligochaete, Lumbriculus variegatus, showed 100% survival in all exposures down to the lowest concentration tested, 0.7 mg O(2)l(-1). Midge (Chironomus dilutus) larva showed a more pronounced response; while survival was less than 90% only below 1.0mg O(2)l(-1), the biomass endpoint showed EC(50), EC(20), and EC(10) values of 1.00 (0.91-1.10), 1.41 (1.16-1.71), and 1.67 (1.25-2.24) mg O(2)l(-1). The amphipod, Hyalella azteca, showed no adverse effects at concentrations as low as 2.12 mg O(2)l(-1). The combination of these data with other literature data suggest that DO minima in current North American 10-d sediment test guidelines are reasonable.     

Geochemical stability of phosphorus solids below septic system infiltration beds

Review of 10 mature septic system plumes in Ontario, revealed that phosphorus (P) attenuation commonly occurred close to the infiltration pipes, resulting in discrete narrow intervals enriched in P by a factor of 2-4 (. MSc thesis, Dept. Earth Sci., University of Waterloo, Waterloo, Ont.; Ground Water 36 (1995) 1000; J. Contam. Hydrol. 33 (1998) 405). Although these attenuation reactions appeared to be sustainable under present conditions, the potential for remobilization of this P mass, should geochemical conditions change, is unknown. To test the stability of these P solids, dynamic flow column tests were carried out using sediments from three of the previously studied sites (Cambridge, Langton and Muskoka) focusing on sediments from the 'High-P' and underlying (Below) zones. Tests were continued for 166-266 pore volumes (PVs), during which time varying degrees of water saturation were maintained. During saturated flow conditions, relatively high concentrations of PO4 were eluted from the Cambridge and Langton High-P zones (up to 4 and 9 mg/l P, respectively), accompanied by elevated concentrations of Fe (up to 1.4 mg/l) and Mn (up to 4 mg/l) and lower values of Eh (<150 mV). The Below zones from Cambridge and Langton, however, maintained lower concentrations of P (generally<2 mg/l), Fe (<0.2 mg/l) and Mn (<1 mg/l) and maintained higher Eh (>250 mV) during saturated flow conditions. During unsaturated flow, P and Fe declined dramatically in the High-P zones (P<1 mg/l, Fe<0.2 mg/l), whereas concentrations remained about the same during saturated and unsaturated flow in the Below zones. This behavior is at least partly attributed to the development of reducing conditions during saturated flow in the High-P zones, leading to reductive dissolution of Fe (III)-P solids present in the sediments. Reducing conditions did not develop in the Below zones apparently because of lower sediment organic carbon (OC) contents (0.03-0.04 wt.%) compared to the High-P zones (0.2-0.65 wt.%). At the Muskoka site, where the sediments were noncalcareous, low values of P (<0.2 mg/l) were maintained in both the High-P and Below columns and reducing conditions did not develop. Results indicate the possibility of remobilizing P accumulated below septic system infiltration beds should conditions become more reducing. This could occur if sewage loading patterns change, for example when a seasonal use, lakeshore cottage is converted to a permanent dwelling.     

The use of NTA and EDDS for enhanced phytoextraction of metals from a multiply contaminated soil by Brassica carinata

The potential of nine different species to grow in the presence of metals (As, Cd, Cu, Pb and Zn) and to accumulate them in the shoots was assessed for each metal separately by germination and root length tests, and successively by hydroponic experiments. Of the nine species tested, Brassica carinata was the species that accumulated the highest amounts of metals in shoots without suffering a significant biomass reduction. To further evaluate the potential of B. carinata for chelant-enhanced phytoextraction of a natural, multiply metal-polluted soil (As, Cd, Cu, Pb and Zn), both hydroponic and pot experiments were carried out with nitrilotriacetic acid (NTA) or (S,S)-ethylenediamine disuccinic acid (EDDS) as complexing agents. The hydroponic study with solutions containing the five metals together showed that accumulation of Cd, Cu, Pb and Zn in shoots was higher following EDDS addition compared to NTA. EDDS was more effective than NTA in desorbing Cu, Pb and Zn from the soil, whereas As and Cd were poorly extracted. B. carinata plants were grown for 4 weeks in the multiply metal-contaminated soil and then the soil was amended with 5 mmol kg(-1) NTA or EDDS. All plants were harvested 1 week after amendment. In comparison to NTA, EDDS was more effective in enhancing the concentrations of Cu, Pb and Zn in B. carinata shoots (2- to 4-fold increase compared to the control). One week after chelant addition, the DTPA-extractable metal concentrations in the polluted soil were lower in the EDDS treatment in comparison with the NTA amendment. Even though B. carinata showed a reduced growth and a relatively low metal uptake, it demonstrated the ability to survive and tolerate the presence of more metals simultaneously.     

Accumulation and depuration of cyanobacterial toxin nodularin and biomarker responses in the mussel Mytilus edulis

Blue mussels (Mytilus edulis) were exposed to an extract made of natural cyanobacterial mixture containing toxic cyanobacterium Nodularia spumigena (70-110 microg nodularin l(-1), 24-h exposure followed by 144-h depuration period in clean water). Toxin concentration increased from initial 400 to 1100 mg kg(-1) after 24-h exposure, measured by liquid chromatography/mass spectrometry (LC/MS). Acetylcholinesterase activity (AChE), a biomarker of direct neurotoxic effects, showed inhibition after 12 and 24h exposure but returned to control level during the depuration period. Catalase (CAT) activity, an indicator of oxidative stress, showed significantly elevated levels in exposed mussels but only 72 h after the end of the exposure. No change in the activity of glutathione-S-transferase (GST) involved in conjugation reactions could be observed. A gradual yet incomplete elimination of nodularin (from 1100 to 600 mg kg(-1)) was observed during the depuration period, and the tissue levels were 30% lower in clean water after 24 h. The observed increase in oxidative stress indicated by elevated CAT activity is likely connected to detoxification reactions leading to the production of reactive oxygen species, including an apparent time lag in this specific enzymatic defence response. That no change in GST activity was observed suggests that this enzyme is not significantly involved in the detoxification process of nodularin-containing cyanobacterial extract in M. edulis.     

Sources of adsorbable organic halogens (AOX) in sludge of Gaza

Average concentrations of adsorbable organic halogens (AOX) in sludge from the Gaza Strip reached 600 mg kg(-1) which currently represents a major limiting factor for sludge application in agriculture. This study aims to identify the main sources of AOX in Gaza where the area is small with limited industrial activities. The results showed that the AOX in effluent sludge is formed mainly inside the treatment plant. Although the plant receives AOX wastewater of only 85 microg l(-1), this value increased five fold inside the plant to an average of 400 microg l(-1) in the effluent wastewater. On the other hand, the sludge from the first sedimentation pond showed an AOX concentration of 213 mg kg(-1) and increased in the final sedimentation pond to 500 mg kg(-1). The AOX concentration in three month old sludge was 130 mg kg(-1). The textile and detergent industries are the major AOX producing industries in Gaza, with an average AOX of 40,000 microg l(-1) in their effluent wastewater. These values do not represent a significant AOX pollution load to the treatment plant because these industries are very limited and their effluents are diluted before entering the municipal treatment plant. Industrial activity decreased in 2006 to less than 70% of the previous four years. Consequently, the AOX in the industrial effluent decreased from 150,000 to 40,000 microg l(-1) over the same time period. Sludge from these industries showed 1300 mg kg(-1) AOX for the past four years and only 400 mg kg(-1) in 2006. Moreover, the AOX in the influent wastewater discharged to the treatment plant decreased from 320 to 85 microg l(-1) for the same period. This study revealed that the major AOX is formed inside the treatment plant and especially in the anaerobic facilities. There was no correlation between the AOX concentrations in the sludge and the wastewater at the same location. Moreover, there was no correlation between the AOX in sludge/wastewater and dissolved oxygen, pH and chloride in that treatment plant.     

Studies of mercury pollution in a lake due to a thermometer factory situated in a tourist resort: Kodaikkanal, India

Kodaikkanal, India, suffered mercury contamination due to emissions and waste from a thermometer factory. Kodai Lake is situated to the north of the factory. The present study determined mercury in waters, sediment and fish samples and compared the values with those from two other lakes, Berijam and Kukkal. Total mercury (Hg(T)) of 356-465 ng l(-1), and 50 ng l(-1) of mercury in methyl mercury form were seen in Kodai waters while Berijam and Kukkal waters showed significantly lower values. Kodai sediment showed 276-350 mg/kg Hg(T) with about 6% methyl mercury. Berijam and Kukkal sediments showed Hg(T) of 189-226 mg/kg and 85-91 mg/kg and lower methylation at 3-4% and 2%, respectively. Hg(T) in fish from Kodai lake ranged from 120 to 290 mg/kg. The results show that pollution of the lake has taken place due to mercury emissions by the factory.     

Influence of sediment on the fate and toxicity of a polyethoxylated tallowamine surfactant system (MON 0818) in aquatic microcosms

The fate and toxicity of a polyethoxylated tallowamine (POEA) surfactant system, MON 0818, was evaluated in water-sediment microcosms during a 4-d laboratory study. A surfactant solution of 8 mg l(-1) nominal concentration was added to each of nine 72-l aquaria with or without a 3-cm layer of one of two natural sediments (total organic carbon (TOC) 1.5% or 3.0%). Control well water was added to each of nine additional 72-l aquaria with or without sediment. Water samples were collected from the microcosms after 2, 6, 24, 48, 72, and 96 h of aging to conduct 48-h toxicity tests with Daphnia magna and to determine surfactant concentrations. Elevated mortality of D. magna (43-83%) was observed in overlying water sampled from water-only microcosms throughout the 96-h aging period, whereas elevated mortality (23-97%) was only observed in overlying water sampled from water-sediment microcosms during the first 24h of aging. Measured concentrations of MON 0818 in water-only microcosms remained relatively constant (4-6 mg l(-1)) during the 96-h period, whereas the concentrations in overlying water from microcosms containing either of the two types of sediment dissipated rapidly, with half-lives of 13 h in the 3.0% TOC sediment and 18 h in the 1.5% TOC sediment. Both toxicity and the concentration of MON 0818 in overlying water decreased more rapidly in microcosms containing sediment with the higher percent TOC and clay and with a higher microbial biomass. Mortality of D. magna was significantly correlated with surfactant concentrations in the overlying water. These results indicate that the toxicity of the POEA surfactant in water rapidly declines in the presence of sediment due to a reduction in the surfactant concentration in the overlying water above the sediment.     

Labile and non-labile desorption rate constants for 33 PCB congeners from lake sediment suspensions

Lake sediments contaminated with polychlorinated biphenyls (PCBs) were purged using a gas stripping technique to estimate desorption rate constants. Desorption profiles and modeling of the data clearly show a two-step release of PCBs from sediment suspensions that can be described as a labile (fast) release followed by a non-labile (slow) release. Data are summarized by labile and non-labile rate constants and by mass in each phase as a function of suspended solids concentration for twelve pure congeners and nine co-eluting data sets (twenty-one chromatograph peaks total). Labile desorption rate constants range from 113 days(-1) to 1.43 days(-1) for the 100 mg/l sediment suspension, from 67.7 days(-1) to 2.45 days(-1) for the 1000 mg/l sediment suspension, and from 8.41 days(-1) to 0.946 days(-1) for the 5000 mg/l sediment suspension. Labile rate constants consistently decreased with increasing suspended solids, and, in general, decreased with increasing degree of chlorination (reflected in increasing retention time in the chromatogram). No consistent trend was observed for the non-labile rate constants with suspended solids concentration or degree of chlorination. The average non-labile rate constant for the PCB congeners studied here was 0.154 days(-1) (s.d.=0.158; n=63). The distribution between the labile and non-labile phases also failed to indicate dependence on suspended solids concentration, chlorine substitution pattern, or molecular weight of the congener, although the data from the 5000 mg/l suspension consistently contained less labile components. The average distributions (n=63) were 60.1% in the labile phase and 39.9% in the non-labile phase.     

Microbial activity in a combined UASB-activated sludge reactor system

A combined upflow anaerobic sludge bed-activated sludge (UASB-AS) reactor system with consistently wasting of excess biomass was used to treat suspended-solids pre-settled piggery wastewater (COD=2000 mg l(-1), total Kjeldahl nitrogen TKN=400 mg l(-1), suspended solids=250-400 mg l(-1)). Thus, the activity of nitrogen-related microbial groups in each individual bioreactor was investigated. When the granules retention time (GRT) of 20-50 d in the UASB reactor, the solids retention time (SRT) of 10-25 d in the AS reactor and the recycle-to-influent ratio (Re) of 1 were maintained, the combined system removed 95-97% of chemical oxygen demand (COD), 100% of TKN and 54-55% of total nitrogen (TN). Denitrification and methanogenesis occurred in the UASB reactor so that both biochemical processes contributed to most of the COD removal and, complete nitrification (most of the TKN removal) occurred in the AS reactor. Compact granules with good settling abilities developed in the UASB reactor, and rapid rates of granulation of break-up granules in the UASB reactor were confirmed by experiments. The activity of nitrifiers and denitrifiers (an=0.68-0.87; adn=0.55-0.70) and the calculated specific nitrification and denitrification rates (qn=0.26-0.47 mg NH4+ -N mg VSS(-1)d(-1); qdn=0.046-0.076 mg NOx- -N mg VSS(-1)d(-1)) significantly increased with decreasing SRT and GRT, respectively. Accordingly, the combined UASB-AS reactor system should be regarded a promising alternative for the removal of organic carbon and nitrogen from piggery wastewater.     

An assessment of the suitable operating conditions for the CeO2/gamma-Al2O3 catalyzed wet air oxidation of phenol

It has been shown that the CeO2/gamma-Al2O3 catalyst is a feasible alternative to CeO2 for the catalytic wet air oxidation (CWAO) of phenol because it remains an effective catalyst and yet is cheaper to prepare. In this study, we found that the optimal cerium content in the CeO2/gamma-Al2O3 catalyst was 20 wt.%, regardless of catalyst loading. Furthermore, at 180 degrees C, with a phenol concentration of 1000 mg l(-1), and an O2 partial pressure of 1.0M Pa or 1.5M Pa, the optimal catalyst loading was 3.0 gl (-1). The efficacy of CWAO of phenol improved with O2 partial pressure, although the effects of O2 pressure were more significant between 0.5 MPa and 1.5 MPa than between 1.5 MPa and 2.0 MPa. After 2 h of reaction, approximately 100% phenol conversion and 80% total organic carbon (TOC) removal was recorded at 180 degrees C, 1000 mg l(-1) of phenol and 3.0 g l(-1) of catalyst. Because these percentages subsequently leveled off, it is suggested that 2 h is a suitable time over which to run the reaction. The efficacy of CWAO of phenol decreased as initial phenol concentration was raised (from 400 to 2500 mg l(-1)), with the exception of phenol conversion after about 2 h, for which 400 mg l(-1) produced the lowest phenol conversion figure. Higher phenol concentrations require both catalyst loading and O2 partial pressure to be increased to maintain high performance. For example, for 2000 mg l(-1) and 2500 mg l(-1) phenol, nearly 100% phenol conversion and 90% TOC removal after 4 h of reaction at 180 degrees C required 4.0 g l(-1) of catalyst and 2.0 MPa.     

Effect of overlying water pH, dissolved oxygen, salinity and sediment disturbances on metal release and sequestration from metal contaminated marine sediments

Experiments were undertaken to examine the key variables affecting metal release and sequestration processes in marine sediments with metal concentrations in sediments reaching up to 86, 240, 700, and 3000 mg kg(-1) (dry weight) for Cd, Cu, Pb and Zn, respectively. The metal release and sequestration rates were affected to a much greater extent by changes in overlying water pH (5.5-8.0) and sediment disturbance (by physical mixing) than by changes in dissolved oxygen concentration (3-8 mg l(-1)) or salinity (15-45 practical salinity units). The physical disturbance of sediments was also found to release metals more rapidly than biological disturbance (bioturbation). The rate of oxidative precipitation of released iron and manganese increased as pH decreased and appeared to greatly influence the sequestration rate of released lead and zinc. Released metals were sequestered less rapidly in waters with lower dissolved oxygen concentrations. Sediments bioturbated by the benthic bivalve Tellina deltoidalis caused metal release from the pore waters and higher concentrations of iron and manganese in overlying waters than non-bioturbated sediments. During 21-day sediment exposures, T. deltoidalis accumulated significantly higher tissue concentrations of cadmium, lead and zinc from the metal contaminated sediments compared to controls. This study suggests that despite the fact that lead and zinc were most likely bound as sulfide phases in deeper sediments, the metals maintain their bioavailability because of the continued cycling between pore waters and surface sediments due to physical mixing and bioturbation.     

Distribution of alkylphenols in the Pearl River Delta and adjacent northern South China Sea, China

The occurrence of alkylphenols (APs) was investigated in surface water and sediments from the Pearl River Delta and adjacent northern South China Sea. Most of the water samples contained detectable amounts of APs, ranging up to 0.628 microg l(-1) for nonylphenol (NP) and 0.068 microg l(-1) for octylphenol (OP). APs were found in all of the sediment samples with concentrations ranging from 59 to 7808 microg kg(-1) for NP and from 1 to 93 microg kg(-1) for OP. The Zhujiang River showed the highest concentrations of APs in both water and sediments. Significant decrease of APs concentrations going from the Zhujiang River to the Shiziyang River was observed. The Xijiang River contained concentrations of APs slightly higher in water but relatively lower in sediments than the Lingding Bay, which might be attributed to their different hydrodynamic and sedimentary characteristics. There was a decreasing trend of APs in water from the rivers to the estuary and further to the sea on the whole. In the Lingding Bay and its outer waters, concentrations of APs in sediments increased to a maximum and then decrease seaward, which was consistent with the distribution trend of the sediment organic carbon contents. Linear regression analyses showed the concentrations of APs were markedly correlated with the sediment organic carbon contents, indicating that the sediment organic carbon is an important factor controlling the levels of APs in sediments.     

Silicon-mediated enhancement of cadmium tolerance in maize (Zea mays L.) grown in cadmium contaminated soil

Pot experiments were performed to study the alleviative effects of exogenous silicon (Si) on cadmium (Cd) phytotoxicity in maize grown in an acid soil experimentally contaminated with Cd. Five treatments were investigated in the first trial consisting of a control (neither Cd nor Si added), Cd added at 20 or 40 mg kg(-1) Cd without or with Si added at 400 mg kg(-1) Si. A following-up trial was conducted with almost the same treatments as in the first trial except that Si was incorporated at 50 mg kg(-1) Si. The results showed that Cd treatment significantly decreased shoot and root dry weight, while addition of Si at both levels significantly enhanced biomass. Addition of Si at 400 mg kg(-1) Si significantly increased soil pH but decreased soil Cd availability, thus reducing Cd concentration in the shoots and roots and total Cd in the shoots. Moreover, more Cd was found to be in the form of specific adsorbed or Fe-Mn oxides-bound fraction in the Si-amended soil. In contrast, soil pH, available Cd and Cd forms were unaffected by addition of Si at 50 mg kg(-1) Si, but shoot Cd concentration in the Si-amended Cd treatments significantly decreased at both Cd levels used compared to the non-Si-amended Cd treatments. Total Cd in the shoots and roots was considerably and significantly higher in the Si-amended Cd treatments than in the non-Si-amended Cd treatments. The xylem sap significantly increased but Cd concentration in the xylem sap significantly decreased in the Si-amended Cd treatments compared with the non-Si-amended Cd treatments irrespective of Cd and Si levels used. The results suggest that Si-enhanced tolerance to Cd can be attributed not only to Cd immobilization caused by silicate-induced pH rise in the soils but also to Si-mediated detoxification of Cd in the plants.     

Effect of EDTA and NTA on cadmium distribution and translocation in Pennisetum purpureum Schum cv. Mott

The primary objective of this research was to investigate the cadmium (Cd) distribution in Pennisetum purpurem (Napier grass) in the presence of 30 mg/L of Cd and different types and concentrations of chelating agents (ethylenediaminetetraacetic acid disodium dihydrate (EDTA), nitrilotriacetic acid (NTA), and EDTA-NTA mixtures). Plant samples were collected every 15 d during a 105-d experimental period. Accumulation of Cd in each part of the plant was determined using atomic absorption spectrometer (AAS), and the distribution of Cd was determined by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) and synchrotron radiation micro X-ray fluorescence (SR-micro-XRF). The highest concentrations of Cd accumulation of 889?±?53 mg kg^?1 in the underground part (roots) and 265?±?26 mg kg^?1 in the aboveground part (stems and leaves) in the presence of 1:1 M ratio of Cd:EDTA after 30 d of exposure were observed. Plants grown in the presence of either NTA or EDTA-NTA mixtures showed significant lower Cd accumulation levels. The LA-ICP-MS analysis showed that Cd was primarily accumulated in the aboveground part (stems and leaves), especially in the xylem and intercalary meristem. In addition, translocation factor was very low. Thus, P. purpurem could be considered as a candidate plant for cadmium phytostabilization.

     

Effect of temperature on the disappearance of four triazine herbicides in environmental waters

The influence of temperature on the disappearance of four s-triazine herbicides, terbuthylazine, simazine, atrazine and prometryn was studied in sea, river and groundwaters spiked with approx. 5 mg l(-1) of each during long-term laboratory incubation. Residues were analyzed by GC-NPD and confirmed by GC-MSD. No clean-up was necessary and a micro on-line method for the determination of herbicide residues was used. The results showed that temperature had little effect on the behaviour of the four herbicides in river and seawaters but strongly affected their behaviour in groundwater. Simazine was the most readily affected compound in sea, river and groundwaters, while terbuthylazine and atrazine were the most persistent in all cases, especially in riverwater. Half-lives ranged from 41 days (constant rate = 0.017 days(-1)) to 196 days (constant rate = 0.003 days(-1)) for simazine (40 degrees C) and terbuthylazine (20 degrees C), respectively, in riverwater. Only for terbuthylazine in riverwater was the remaining percentage at the end of the experiment higher than 50% (58%, 3.21 mg l(-1)). In the other cases, the remaining percentage varied from 4% (0.20 mg l(-1), 40 degrees C) to 43% (2.25 mg l(-1), 20 degrees C) for simazine and terbuthylazine, respectively, in groundwater.     

The spatial variability of nitrogen and phosphorus concentration in a sand aquifer influenced by onsite sewage treatment and disposal systems: a case study on St. George Island, Florida

Groundwater from a shallow freshwater lens on St. George Island, a barrier island located in the Panhandle of Florida, eventually discharges into Apalachicola Bay or the Gulf of Mexico. Nutrient concentrations in groundwaters were monitored downfield from three onsite sewage treatment and disposal systems (OSTDS) on the island. Estimates of natural groundwater nutrient concentrations were obtained from an adjacent uninhabited island. Silicate, which was significantly higher in the imported drinking water relative to the surficial aquifer on St. George Island (12.2+/-1.9 mg Si l(-1) and 2.9+/-0.2 mg Si l(-1), respectively), was used as a natural conservative tracer. Our observations showed that nitrogen concentrations were attenuated to a greater extent than that of phosphorus relative to the conservative tracer. At the current setback distance (23 m), both nitrogen and phosphate concentrations are still elevated above natural levels by as much as 2 and 7 times, respectively. Increasing the setback distance to 50 m and raising the drainfields 1 m above the ground surface could reduce nutrient levels to natural concentrations (1.1+/-0.1 mg N l(-1), 0.20+/-0.02 mg P l(-1)).     

Distribution of polycyclic aromatic hydrocarbons in water and surface sediments from Daya Bay,China

Marine culture is thriving in China and represents a major component of the regional economy in coastal zones, yet the environmental quality of many of those areas has never been studied. This paper attempts to investigate the quality status of Daya Bay, a key aquaculture area in China. The levels of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in water and sediment samples of the bay. The total concentrations of 16 PAHs varied from 4228 to 29325 ng l(-1) in water, and from 115 to 1134 ng g(-1) dry weight in sediments. In comparison to many other marine systems studied, the PAH levels in Daya Bay waters were relatively high, and at six sites they were sufficiently high (> 10 microg l (-1)) to cause acute toxicity. The PAH composition pattern in sediments suggest dominance by medium to high molecular weight compounds, and the ratio of certain related PAHs indicate important pyrolytic and petrogenic sources. Further analysis showed that the distribution coefficient (KD) increased with the particular organic carbon content of sediments, consistent with the PAH partition theory. The organic carbon normalised distribution coefficient (K(oc)) also increased with the compounds' octanol/water partition coefficient (K(ow)), confirming the potential applicability of the linear free energy relationships in the modelling and prediction of PAH behaviour in marine environments.