Methodological factors influencing inhalation bioaccessibility of metal(loid)s in PM2.5 using simulated lung fluid.

In this study, methodological factors influencing the dissolution of metal(loid)s in simulated lung fluid (SLF) was assessed in order to develop a standardised method for the assessment of inhalation bioaccessibility in PM2.5. To achieve this aim, the effects of solid to liquid (S/L) ratio (1:100 to 1:5000), agitation (magnetic agitation, occasional shaking, orbital and end-over-end rotation), composition of SLF (artificial lysosomal fluid: ALF; phagolysosomal simulant fluid: PSF) and extraction time (1-120 h) on metal(loid) bioaccessibility were investigated using PM2.5 from three Australian mining/smelting impacted soils and a certified reference material. The results highlighted that SLF composition significantly (p < 0.001) influenced metal(loid) bioaccessibility and that when a S/L ratio of 1:5000 and end-over-end rotation was used, metal(loid) solubility plateaued after approximately 24 h. Additionally, in order to assess the exposure of metal(loid)s via incidental ingestion of surface dust, PM2.5 was subjected to simulated gastro-intestinal tract (GIT) solutions and the results were compared to extraction using SLF. Although As bioaccessibility in SLF (24 h) was significantly lower than in simulated GIT solutions (p < 0.05), Pb bioaccessibility was equal to or significantly higher than that extracted using simulated GIT solutions (p < 0.05).

An inhalation-ingestion bioaccessibility assay (IIBA) for the assessment of exposure to metal(loid)s in PM10.

Although metal(loid) bioaccessibility of ambient particulate matter, with an aerodynamic diameter of <10µm (PM10), has recently received increasing attention, limited research exists into standardising in-vitro methodologies using simulated lung fluid (SLF). Contradictions exist regarding which assay parameters should be adopted. Additionally, potential continuation of metal(loid) dissolution once PM10 is cleared from the lungs and passed through the gastro-intestinal tract (GIT) has rarely been addressed. The objective of this study was to assess parameters that influence inhalation bioaccessibility in order to develop a conservative assay that is relevant to a human inhalation scenario. To achieve this aim, the effect of solid to liquid (S/L) ratio, extraction time, agitation and five major SLF compositions on the bioaccessibilities of arsenic (As) and lead (Pb) was investigated using PM10 from three Australian mining/smelting impacted regions. Using the biologically relevant parameters that resulted in the most conservative outcomes, bioaccessibility of metal(loid)s in PM10 was assessed in SLF, followed by simulated GIT solutions. Results from this study revealed that fluid composition and S/L ratio significantly affected metal(loid) dissolution (p<0.05). The highest Pb bioaccessibility resulted using simulated lung-gastric solution, while that of As resulted using simulated lung-gastric-small intestinal tract solutions. Compared to SLF alone, metal(loid) dissolution using the inhalation-ingestion bioaccessibility assay (IIBA) was significantly higher (p<0.05) for all PM10 samples.

Arsenic distribution and bioaccessibility across particle fractions in historically contaminated soils.

Incidental soil ingestion is a common contaminant exposure pathway for humans, notably children. It is widely accepted that the inclusion of total soil metal concentrations greatly overestimates the risk through soil ingestion for people due to contaminant bioavailability constraints. The assumption also assumes that the contaminant distribution and the bioaccessible fraction is consistent across all particle sizes. In this study, we investigated the distribution of arsenic across five particle size fractions as well as arsenic bioaccessibility in the <250-, <100-, <10- and 2.5-microm soil particle fractions in 50 contaminated soils. The distribution of arsenic was generally uniform across the larger particle size fractions but increased markedly in the <2.5-microm soil particle fraction. The marked increase in arsenic concentration in the <2.5-microm fraction was associated with a marked increase in the iron content. Arsenic bioaccessibility, in contrast, increased with decreasing particle size. The mean arsenic bioaccessibility increased from 25 +/- 16% in the <250-microm soil particle fraction to 42 +/- 23% in the <10-microm soil particle fraction. These results indicate that the assumption of static arsenic bioaccessibility values across particle size fractions should be reconsidered if the ingested material is enriched with small particle fractions such as those found in household dust.

Arsenic uptake and speciation in vegetables grown under greenhouse conditions.

The accumulation of arsenic (As) by vegetables is a potential human exposure pathway. The speciation of As in vegetables is an important consideration due to the varying toxicity of different As species. In this study, common Australian garden vegetables were hydroponically grown with As-contaminated irrigation water to determine the uptake and species of As present in vegetable tissue. The highest concentrations of total As were observed in the roots of all vegetables and declined in the aerial portions of the plants. Total As accumulation in the edible portions of the vegetables decreased in the order radish >> mung bean > lettuce = chard. Arsenic was present in the roots of radish, chard, and lettuce as arsenate (As(V)) and comprised between 77 and 92% of the total As present, whereas in mung beans, arsenite (As(III)) comprised 90% of the total As present. In aerial portions of the vegetables, As was distributed equally between both As(V) and As(III) in radish and chard but was present mainly as As(V) in lettuce. The presence of elevated As in vegetable roots suggests that As species may be complexed by phytochelatins, which limits As translocation to aerial portions of the plant.

Arsenic uptake and speciation in rice plants grown under greenhouse conditions with arsenic contaminated irrigation water.

The accumulation of arsenic (As) by rice (Oryza sativa L.) is of great interest considering the dietary intake of rice is potentially a major As exposure pathway in countries where rice is irrigated with As contaminated groundwater. A small scale rice paddy experiment was conducted to evaluate the uptake of As by rice. Arsenic concentrations in rice tissue increased in the order grain<

Microbial activity and phospholipid fatty acid pattern in long-term tannery waste-contaminated soil.

We investigated the phospholipid fatty acid (PLFA) pattern and dehydrogenase activity (DHA) in soil samples from three sites (designated as low, medium, and high based on the level of chromium) in a long-term (25 years after last waste input) tannery waste-contaminated area rich in Cr. Soil samples, collected from different soil depths (0-100 cm), at each site were used in this study. In general, soil samples from all three contaminated sites had elevated pH, electrical conductivity, organic carbon (OC), total Cr, and hexavalent Cr [Cr(VI)]. The maximum total Cr concentration in surface soils (0-10 cm) at the highly contaminated site was 102 gkg(-1), with 4.6 mgkg(-1) present as the bioavailable water-soluble Cr. More than 50% of soluble Cr was in the form of Cr(VI) (2.7 mgkg(-1)). DHA (normalized to OC) was inhibited to a greater extent in soil samples from the highly contaminated site than in low- and medium-contaminated soil samples. PLFA analyses of surface soils indicated that there was a shift in PLFA patterns. PLFAs specific for bacteria (i15:0, a15:0, 15:0, i16:0, a17:0, and cy17:0) decreased significantly (P<0.01) with an increase in Cr contamination. Among the bacterial PLFAs, 15:0, i16:0 and a17:0 had a significant negative correlation with contamination including bioavailable Cr(VI) in soil solution. To our knowledge, this is the first report of alterations in the PLFA profile in soils due to long-term tannery waste pollution.

Biosorption of organochlorine pesticides using fungal biomass.

Cladosporium strain AJR(3)18501 was tested for its ability to sorb the organochlorine pesticide (OCP) p,p'-DDT from aqueous media. When p,p'-DDT was added to distilled water, ethanol or 1-propanol solutions in excess of its solubility, p,p'-DDT was sorbed onto the fungal biomass. Increasing the amount of p,p'-DDT in solution by changing the medium composition increased sorbent uptake: p,p'-DDT uptake by the fungal biomass was 2.5 times greater in 25% 1-propanol (17 mg of p,p'-DDT g(-1) dry weight fungal biomass) than in distilled water. When p,p'-DDT was dissolved in 25% 1-propanol (12 mg x l(-1)), rapid p,p'-DDT sorption occurred during the first 60 min of incubation. p,p'-DDT in solution was reduced to 2.5 mg x l(-1) with the remaining p,p'-DDT recovered from the fungal biomass. A number of environmental parameters were tested to determine their effect on p,p'-DDT biosorption. As arsenic (As) is prevalent at DDT-contaminated cattle dip sites, its effect on p,p'-DDT uptake was determined. The presence of As [As(III) or As(V) up to 50 mg x l(-1)] did not inhibit p,p'-DDT uptake and neither As species could be sorbed by the fungal biomass. Changing the pH of the medium from pH 3 to 10 had a small effect on p,p'-DDT sorption at low pH indicating that an ion exchange process is not the major mechanism for p,p'-DDT sorption. Other mechanisms such as Van der Waals forces, chemical binding, hydrogen bonding or ligand exchange may be involved in p,p'-DDT uptake by Cladosporium strain AJR(3)18501.

Metabolite repression inhibits degradation of benzo[a]pyrene and dibenz[a,h]anthracene by Stenotrophomonas maltophilia VUN 10,003.

Large inocula of Stenotrophomonas maltophilia VUN 10,003 were used to investigate bacterial degradation of benzo[a]pyrene and dibenz[a,h]anthracene. Although strain VUN 10,003 was capable of degrading 10-15 mg (-1) of the five-ring compounds in the presence of pyrene after 63 days, further addition of pyrene after degradation of the five-ring polycyclic aromatic hydrocarbons (PAHs) ceased did not stimulate significant decreases in the concentration of benzo[a]pyrene or dibenz[a,h]anthracene. However, pyrene was degraded to undetectable levels 21 days after its addition. The amount of benzo[a]pyrene and dibenz[a,h]anthracene degraded by strain VUN 10,003 was not affected by the initial concentration of the compounds when tested at 25-100 mg l(-1), by the accumulation of by-products from pyrene catabolism or a loss of ability by the cells to catabolise benzo[a]pyrene or dibenz[a,h]anthracene. Metabolite or by-product repression was suspected to be responsible for the inhibition: By-products from the degradation of the five-ring compounds inhibited their further degradation.

Enrichment and isolation of non-specific aromatic degraders from unique uncontaminated (plant and faecal material) sources and contaminated soils.

Microbial analysis of contaminated soil and uncontaminated plant and faecal material resulted in the enrichment of a number of microbial communities capable of utilizing a range of environmental pollutants. Growth was observed on polycyclic aromatic hydrocarbons, polychlorinated biphenyls, heterocyclic aromatic compounds and organochlorine pesticides. However, none of the communities could grow on pentachlorophenol. Pure cultures were isolated from microbial communities using phenanthrene and pyrene as the sole carbon and energy source. Isolates were also obtained using DDT, DOH, DBH and PCPA when peptone was supplemented to the medium. Strain AJR39,504, isolated using DDT and peptone, could not be positively identified on the basis of substrate utilization tests. However, it most closely resembled Stenotrophomonas maltophilia (0.424 similarity) using the Microlog 3 database software. Isolate AJR39, 504 could also grow on polycyclic aromatic hydrocarbons, chlorinated- and nitro-aromatic compounds. In addition, the degradation of DDT (100 mg l(-1)) by isolate AJR39,504 resulted in a 35% decrease in DDT concentration after 28 days with a concomitant increase in DDD concentration.

Microbial degradation and detoxification of high molecular weight polycyclic aromatic hydrocarbons by Stenotrophomonas maltophilia strain VUN 10,003.

The ability of Stenotrophomonas maltophilia strain VUN 10,003 to degrade and detoxify high molecular weight polycyclic aromatic hydrocarbons (PAHs) was evaluated in a basal liquid medium. Using high cell density inocula of strain VUN 10,003, the concentration of pyrene, fluoranthene, benz[a]anthracene, benzo[a]pyrene, dibenz[a, h]anthracene and coronene decreased by 98, 45, 26, 22, 22 and 55% over periods ranging from 5 to 42 d. When a PAH mixture containing three- to seven-ring compounds was used, degradation of both low and high molecular weight compounds occurred concurrently. Mutagenicity assays (Ames Test) demonstrated a decrease in the mutagenic potential of dichloromethane culture extracts from all cultures containing single PAH over the incubation period, corresponding to the decrease in the concentration of the PAH. These observations indicate that strain VUN 10,003 could be used for the detoxification of PAH-contaminated wastes.

Extraction and recovery of organochlorine pesticides from fungal mycelia.

An extraction method was developed to recover organochlorine pesticides (OCPs) associated with live and mercuric chloride-treated fungal mycelia. A Cladosporium sp. was inoculated into potato dextrose broth, DDT (90 mg/l) added and incubated for seven days. The combination of a microextraction procedure for aqueous-phase-associated DDT and a sonication extraction for mycelia-bound DDT, using dichloromethane as the extracting solvent, resulted in the recovery of 31-51% of added DDT. DDT recovery was increased to 62-65% by grinding the fungal mycelia before sonication. Alkali and nitric acid pretreatments were tested to increase the recovery of DDT associated with fungal mycelia, however, these treatments resulted in the production of unidentified DDT transformation products. Pretreating mycelia containing DDT in concentrated hydrochloric acid at 60 degrees C for 2, 4 and 6 h resulted in DDT recoveries of 90-91%, 99% and 101-102% respectively without the production of transformation products. When an OCP mixture (DDT, DDD and DDE) was added to fungal mycelia, between 89% and 96% of DDT, DDD and DDE were recovered from live cultures compared to 85-91% in mercuric chloride-treated cultures using the microextraction/hydrochloric acid pretreatment (60 degrees C/6 h) sonication extraction method.