A novel bioaccessibility prediction method for PAHs in soil: Composite extraction with hydroxypropyl-ß-cyclodextrin and extracellular polymer substances.

Hydroxypropyl-ß-cyclodextrin (HPCD) extraction has been widely used to estimate bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in soil, but it often underestimates the actual risk due to lack of information regarding the exogenous active substances, such as extracellular polymer substance (EPS) secreted by microorganisms. In this study, a novel technique, composite extraction of HPCD each with rhamnolipid (RL), bovine serum albumin (BSA) and alginate sodium (AS), models of lipopolysaccharide, proteins and polysaccharides, was developed to assess PAHs bioaccessibility to earthworms. In addition, comparisons were conducted with accelerated solvent extraction (ASE) and individual HPCD extraction. The results demonstrated that all chemical extractions were linearly correlated with earthworm accumulation, and individual HPCD extraction underestimated PAH bioaccessibility by about two times. However, the overall performances of the three composite chemical extractions (HPCD/AS, HPCD/RL, HPCD/BSA) were better than individual HPCD extraction, among which, HPCD/AS was best at estimating the earthworm accumulation (considering both correlation coefficient and fitted linear slope). Therefore, all observations implied that HPCD/AS extraction could be used as a fast and reliable method to predict PAH bioaccessibility to earthworms in contaminated soils.

[Prediction of PAHs Bioavailability in Spiked Soil by Composite Extraction with Hydroxypropyl-ß-cyclodextrin and Rhamnolipid].

In this study, composite extraction of hydroxypropyl-ß-cyclodextrin (HPCD) with rhamnolipid (RL) was selected to assess the bioavailability of polycyclic aromatic hydrocarbons (PAHs) to earthworms in red soil from Hainan, China, spiked with phenanthrene (Phe), pyrene (Pyr) and benzo (a) pyrene (BaP). The results showed that when RL was more than the critical micelle concentration, apparent solubility of PAHs increased due to micellar solubilization of RL. So more PAHs were desorbed from solid phase of soil. Real biological experiments showed that there was a good linear relationship between earthworm-accumulated PAHs and HPCD/RL-extracted PAHs (R2=0.98, n=15). However, earthworm-accumulated PAHs was 2.04 times higher than HPCD-extracted PAHs, but only 1.15 times higher than HPCD/RL-extracted PAHs. This indicated that HPCD/RL was more actual and reliable than HPCD in the assessment of PAHs bioavailability to earthworms. Therefore, the addition of RL, to some extent, enhanced the prediction ability of HPCD in PAHs bioavailability, which might provide a new direction and implications in risk assessment and bioremediation of organic contaminants.

[Aging Law of PAHs in Contaminated Soil and Their Enrichment in Earthworms Characterized by Chemical Extraction Techniques].

To evaluate the effect of aging on the availability of PAHs, chemical extraction by exhaustive ( ASE extraction) and nonexhaustive techniques (Tenax-TA extraction, hydroxypropyl-p-cyclodextrin ( HPCD ) extraction, n-butyl alcohol ( BuOH) extraction) as well as PAHs accumulation in earthworms (Eisenia fetida) were conducted in yellow soil from Baguazhou, Nanjing, China, and red soil from Hainan, China, spiked with phenanthrene, pryene and benzo(a) pyrene and aged 0, 7, 15, 30 and 60 days. The results showed that the concentration of PAHs extracted by ASE and three nonexhaustive techniques and accumulated by earthworms significantly decreased with aging time, except the ASE extracted concentration between 30-and 60-day aging time. Furthermore, the relationships were studied in this experiment between chemical extracted PAHs concentration and accumulated concentration in earthworms. PAHs accumulated concentration in earthworms was not significantly correlated with the exhaustive extracted concentration of PAHs in soil (R² 0.44-0.56), which indicated that ASE extraction techniques could not predict PAHs bioavailability to earthworms because it overestimated the risk of PAHs. However, the PAHs accumulated concentration in earthworms was significantly correlated with the three nonexhaustive extracted concentrations of PAHs in soil, which indicated that all the three nonexhaustive techniques could predict PAHs bioavailability to earthworm to some extent, among which, HPCD extraction (R² 0.94-0.99) was better than Tenax-TA extraction (R² 0.62-0.87) and BuOH extraction (R² 0.69-0.94). So HPCD extraction was a more appropriate and reliable technique to predict bioavailability of PAHs in soil.

[Effect of sulfur on the species of Fe and As under redox condition in paddy soil].

Redox conditions of the polluted paddy soil with exogenous As were simulated by redox reaction apparatus after flowing N2 and O2 applied with different forms of inorganic sulfur(CK-S0, elemental sulfur-S1 and sulfate-S2). Results showed that redox potential (Eh) was about -100 - -200 mV and the pH 7.0-8.0 and the pe + pH 4-7 in soil solution when flowed N2, and Eh about 200 mV and the pH 6.5-7.5 and pe + pH 9-12 when continuously flowed O2. Concentrations of the dissolved Fe in soil solution were in 1.2-1.6 mg x L(-1) either flowed N2 or O2, and the order of Fe concentrations was AsS0 treatment > AsS1 treatment > AsS2 treatment. Amounts of soil Fe oxide by HCl extraction from different treatments were 5 g · kg(-1) lower than the original soil [(21.4 ± 0.3) g · kg(-1)] when flowed N2, and it was in favor of the transformation of crystal Fe into amorphous iron and Fe2+. Activity of Fe oxides from different treatments increased comparing to that of the original soil (46. 8%), and the order of activity of Fe oxides was AsS2 treatment (49.4%) < AsS1 treatment (60%). Fe2+ in solution and FeS were oxidized into Fe3+, and hydrolysis of Fe3+ was produced into Fe(OH)3 precipitation when flowed O2. It increased the contents of acid-soluble and crystal Fe oxide, and the order of activity of Fe oxides was AsS1 (41.2%) treatment > AsS2 (36.1%) treatment. Concentrations of As in soil solution were in the order of AsS0 [(1.13 ± 0.04) mg · L(-1)] > AsS1 [(0.89 ± 0.01) mg L(- 1)] > AsS2 [ (0.77 ± 0.04 )mg · L(-1)] when flowed N2 and was AsS1 [(0.77 ± 0.01) mg · L(-1)] > AsS0 [(0.20 ± 0.09 ) mg · L(-1)] > AsS2 [(0.09 ± 0.01) mg · L(-1)] when flowed O2. The proportions of arsenic fractions followed the order of the residual phases (34.9%-41.4%) ≈ specifically-sorbed (37.4%-39.5%) > well-crystallized hydrous oxides of Fe/Mn (23.3%-25.6%) > non-specifically sorbed (2.4%-3.3%) > amorphous hydrous oxides of Fe/Mn (0.5%-0.8%) when flowed N2, and was the residual phases (30.8%-39.3%) specifically-sorbed (30.3%-34.7%) > well-crystallized hydrous oxides of Fe/Mn (26.0%-28.7%) > amorphous hydrous oxides of Fe/Mn (9.3%-10.7%) > non-specifically sorbed (0.5%-1.6%) when flowed O2. Arsenic from amorphous hydrous oxides of Fe/Mn raised about 9% by flowing O2 than by flowing N2. This could be the effect of the aging amorphous Fe/Mn on the transformation of As, and the increased activity of iron oxide under reducing conditions and enhanced mobility of Arsenic. Elemental surfer system could increase mobility of arsenic more than sulfate system which may decrease degree of activity of iron oxide.

[Relationship between Fe, Al oxides and stable organic carbon, nitrogen in the yellow-brown soils].

The stable organic carbon and nitrogen of the different particles were gained by oxidation of 6% NaOCl in the yellow-brown soils. The relationships between the contents of selective extractable Fe/Al and the stable organic carbon/nitrogen were investigated. It shown that amounts of dithionite-citrate-(Fe(d)) and oxalate-(Fe(o)) and pyrophosphate extractable (Fe(p)) were 6-60.8 g x kg(-1) and 0.13-4.8 g x kg(-1) and 0.03-0.47 g x kg(-1) in 2-250 microm particles, respectively; 43.1-170 g x kg(-1) and 5.9-14.0 g x kg(-1) and 0.28-0.78 g x kg(-1) in < 2 microm particles, respectively. The contents of oxalate-(Al(o)) and pyrophosphate extractable (Al(p)) were 0.08-1.34 g x kg(-10 and 0.11-0.47 g x kg(-1) in 2-250 microm particles, respectively; 2.96-6.20 g x kg(-1) and 0.38-0.78 g x kg(-1) in < 2 microm particles, respectively. And amounts of selective extractable Fe are generally higher in paddy yellow-brown soils than in arid yellow-brown soils, and that of selective extractable Al are lower in the former than in the latter. Amounts of the stable organic carbon and nitrogen, higher in paddy yellow-brown soils than in arid yellow-brown soils, were 0.93-6.0 g x kg(-1) and 0.05-0.36 g x kg(-1) in 2-250 microm particles, respectively; 6.05-19.3 g x kg(-1) and 0.61-2.1 g x kg(-1) in < 2 microm particles, respectively. The ratio of the stable organic carbon and nitrogen (C(stable)/N(stable)) were 9.50-22.0 in 2-250 microm particles and 7.43-11.54 in < 2 microm particles, respectively. The stabilization index (SI(C) and SI(N)) of the organic carbon and nitrogen were 14.3-50.0 and 11.9-55.6 in 2-250 microm particles, respectively; 53.72-88.80 and 40.64-70.0 in < 2 microm particles, respectively. According to SI, it is lower in arid yellow-brown soils than in paddy yellow-brown soils. The organic carbon and nitrogen are advantageously conserved in paddy yellow-brown soil. An extremely significant positive correlation of the stable organic carbon and nitrogen with selective extractable Fe/Al is observed. The most amounts between the stable organic carbon and nitrogen and selective extractable Fe/Al appear in clay particles, namely the clay particles could protect the soil organic carbon and nitrogen.

[Characteristics of DNA adsorption and desorption in variable and constant charge soil colloids].

The characteristics of adsorption and desorption of DNA by Red soil colloid, Latosol colloid, Chao colloid and Cinnamon colloid at different pH values were studied using a batch method. It showed that there was an increase of solution pH after adsorption of DNA by the four soil colloids in both NaCl and KCl electrolyte systems. The increasing ranges of pH values were in order of Red soil colloid > Latosol colloid > Chao colloid > Cinnamon colloid, and NaCl electrolyte system > KCl electrolyte system. The amounts of DNA adsorption on soil colloids decreased with the increase of pH value. The maximum amounts of DNA adsorption in different colloids were about 13.1-14.8 microg x mg(-1) when pH values were 2-4. The decreasing ranges of the amounts of DNA adsorption were about 5.5 microg x mg(-1) in NaCl electrolyte system and 2.1 Mg x mg(-1) in KCl electrolyte system in Red soil colloid and Latosol colloid after the rising of equilibrium solution pH from 4.2 to 8.6, whereas the remarked decreasing ranges of the adsorption amounts of DNA were about 8.3-12.2 microg x mg(-1) on Chao colloid and Cinnamon colloid in two electrolyte systems. The decreasing ranges of DNA adsorption were in order of the constant charge (Chao soil and Cinnamon) colloids > the variable charge (Red soil and Latosol) colloids. The differences of desorption on the variable and the constant charge colloids are very significant while the DNA adsorbed was desorbed with NaOAc solution and NaH2 PO4 solution. The desorption percent desorption of DNA as NaH2PO4 desorbent was 23.5%-40.2% larger on the variable charge colloids than 8.8%-21.6% on the constant charge of colloids at the three different solution pH values of 3, 5 and 7, while that as NaOAc desorbent was 72.3%-85.9% larger on the constant charge colloids than 10%-24.5% on the variable charge colloids. These results implied that the ligand exchange played a more important role in DNA adsorption on the variable charge colloids, and electrostatic interactions did on the constant charge colloids. This is the differences of DNA adsorption and desorption on different charge colloid surfaces.

[Effects of oxalate on acid phosphatase adsorption and its activity on soil colloids and minerals].

By a batch method, this paper studied the effects of different concentration and pH of oxalate, an important root exudate, on the adsorption of acid phosphatase and its activity on < 2 microm colloids of yellow brown soil and latosol, and on minerals goethite and kaolinite. The results showed that the acid phosphatase adsorption by goethite was less affected by the concentration of oxalate; while the adsorbed amount of this enzyme by the other test colloids and kaolinite was sharply decreased with the increasing oxalate concentration (0-5 mmol x L(-1)) first, and then gradually increased to the level equal to or less than the blank, which may be related to the coordination type of oxalate on soil colloids and minerals, and their surface charge change and dissolution. In the systems oxalate existed, the adsorbed amount of acid phosphatase by soil colloids and minerals decreased in order of goethite >> yellow brown soil > kaolinite > latosol. The pH value for the maximum adsorption of acid phosphatase was between the IEP of the enzyme and the PZC of test colloids and minerals. After the enzyme was immobilized on colloids and minerals, the pH of its maximum specific activity had no change, or shifted to a higher value.

[The influence of simulated acid rain on acidity and K+ leaching regulation of different soil layers].

The influence of simulated acid rain on acidity and K+ release of different soil layers of red soil from Jiangxi was investigated in the lab when surface soil was mixed with KCl. The results indicated that pH of leaching solution first decreased, then increased in the different soil layers, but pH at the beginning moment of leaching existed prominent differences and pH of leachate of pH 2.5 acid rain in A and AB layers again decreased during subsequent stage. There was a peak value of EC of leachate appearing at the beginning stage, it showed that nutrient ions in soil rapidly moved downwards into lower depth of profile. K+ concentration of effluent solution was related to acidity of acid rain and the pH2.5 value of acid rain accelerated K+ transportation downwards along profile. K+ release of A soil layer was divided into two moments which one was the rapid rate of K+ release process at the moment of beginning and then into the middle rate of release process. As to pH 4.5 value of acid rain, it also existed rapid and slow rate processes.