Genotoxicity assessment of soils from wastewater irrigation areas and bioremediation sites using the Vicia faba root tip micronucleus assay

Genotoxicity potential of soils taken from wastewater irrigation areas and bioremediation sites was assessed using the Vicia faba root tip micronucleus assay. Twenty five soils were tested, of which 8 were uncontaminated soils and taken as the control to examine the influence of soil properties; 6 soils were obtained from paddy rice fields with a history of long-term wastewater irrigation; 6 soils were obtained from bioremediation sites to examine effects of bioremediation; and 5 PAH-contaminated soils were used to examine methodological effects between direct soil exposure and exposure to aqueous soil extracts on micronuclei (MN) frequency () in the V. faba root tips. Results indicate that soil properties had no significant influences on MN frequencies (p > 0.05) when soil pH varied between 3.4 to 7.6 and organic carbon between 0.4% and 18.6%. The MN frequency measured in these control soils ranged from 1.6‰ to 5.8‰. MN frequencies in soils from wastewater irrigation areas showed 2- to 48-fold increase as compared with the control. Soils from bioremediation sites showed a mixed picture: MN frequencies in some soils decreased after bioremediation, possibly due to detoxification; whereas in other cases remediated soils induced higher MN frequencies, suggesting that genotoxic substances might be produced during bioremediation. Exposure to aqueous soil extracts gave a higher MN frequency than direct exposure in 3 soils. However, the opposite was observed in the other two soils, suggesting that both exposure routes should be tested in case of negative results from one route. Data obtained from this study indicate that the MN assay is a sensitive assay suitable for evaluating genotoxicity of soils.

Extraction of compounds associated with water repellency in sandy soils of different origin

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C–H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS).

Key findings are: (i) none of organic carbon content, amount of aliphatic C–H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency.

Investigation of compounds causing water repellency in the rhizosphere of sandy soils from a wide range of locations.

Although soils are generally considered to wet readily, some are actually water repellent at the surface and in the rhizosphere. This phenomenon occurs at low to moderate moisture contents and has been reported from soils under a range of vegetation types and from many regions around the globe. Water repellency in soils can have serious environmental implications including reduced seed germination and plant growth as well as irrigation efficiency, accelerated soil erosion, and enhanced leaching of agrochemicals through preferential flow. it has been proposed that water repellency is caused by the accumulation of hydrophobic organic compounds released as root exudates, microbial byproducts or from decomposing organic matter, which are deposited on mineral or aggregate surfaces, or are present as interstitial matter, Few studies to date have attempted to isolate and characterize these compounds and their structure is therefore only poorly understood, These studies have generally focussed on only a single soil or a small range of samples, have not included non-repellent soils as a control and have not always been able to demonstrate that the substances isolated are indeed responsible for repellency formation.

This study reports on the first part (extraction procedures) of a research programme addressing these gaps in current knowledge by investigating a wide range of severely repellent and wettable ‘control’ samples from different countries, and by including assessments of extraction efficiency and ability of extracts to cause repellency. Analytical methods include DRIFT (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) of soils and IR (Infrared) analysis of extracts.

Key findings are that (i) soil sample heating after extraction is valuable in assessing the effectiveness of the extraction procedure, (ii) Soxhlet extraction using isopropanol/ ammonia (70/30 v/v) was the most effective method in extracting hydrophobic compounds, while leaving the ability of extracted compounds to induce water repellency virtually unaffected, (iii) wettable control soils also contain hydrophobic substances capable of inducing water repellency, (iv) the amount of organic compounds extracted was poorly related to sample repellency, indicating that compounds responsible for repellency may only represent a small fraction of the extract, (v) differences in extraction efficiency between different samples indicate that the compounds responsible may differ generically and/or in terms of their bonding to minerals, and (vi) the combination of repellency assessments with DRIFT on soils and JR on extracts used with internal standards has considerable potential to allow quantification of CH bearing organic matter in the soil, the efficiency of extraction processes for its removal, and its significance in causing water repellency in soils.

Quantifying effects of soil heterogeneity on groundwater pollution at four sites in the USA

Four sites located in the north-eastern region of the United States of America have been chosen to investigate the impacts of soil heterogeneity in the transport of solutes (bromide and chloride) through the vadose zone (the zone in the soil that lies below the root zone and above the permanent saturated groundwater). A recently proposed mathematical model based on the cumulative beta distribution has been deployed to compare and contrast the regions' heterogeneity from multiple sample percolation experiments. Significant differences in patterns of solute leaching were observed even over a small spatial scale, indicating that traditional sampling methods for solute transport, for example the gravity pan or suction Iysimeters, or more recent inventions such as the multiple sample percolation systems may not be effective in estimating solute fluxes in soils when a significant degree of soil heterogeneity is present. Consequently, ignoring soil heterogeneity in solute transport studies will likely result in under- or overprediction of leached fluxes and potentially lead to serious pollution of soils and/or groundwater. The cumulative beta distribution technique is found to be a versatile and simple technique of gaining valuable information regarding soil heterogeneity effects on solute transport. It is also an excellent tool for guiding future decisions of experimental designs particularly in regard to the number of samples within one site and the number of sampling locations between sites required to obtain a representative estimate of field solute or drainage flux.

Rearing juvenile Australian native percichthyid fish in fertilised earthen ponds

The post-larvae and fry of Australian native species, including those of species belonging to the family Percichthyidae, are routinely reared to a fingerling size (35-55 mm in length) in fertilised earthen fry rearing ponds. The juveniles of Murray cod (Maccullochella peelii peelii\ trout cod (Maccullochella macquariensis) and Macquarie perch (Macquaria australasicd) (Percichthyidae) are grown in fry rearing ponds at the Marine and Freshwater Resources Institute, Snobs Creek (Vie. Australia) for production of fingerlings for stock enhancement and aquaculture purposes. However, no detailed studies have been undertaken of the productivity of these ponds and factors that influence fish production. An ecologically based study was undertaken to increase the knowledge of pond ecology and dynamics, particularly in relation to the rearing of juvenile Murray cod, trout cod and Macquarie perch in ponds. Over nine consecutive seasons commencing in 1991, water chemistry, plankton, macrobenthos (2 seasons only) and fish were monitored and studied in five ponds located at Snobs Creek. A total of 80 pond fillings were undertaken during the study period. Additional data collected from another 24 pond fillings undertaken at Snobs Creek collected prior to this study were included in some analyses. Water chemistry parameters monitored in the ponds included, temperature, dissolved oxygen pH, ammonia, nitrite, nitrate, orthophosphate and alkalinity. Water chemistry varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Liming of ponds increased the total alkalinity to levels that were considered to be suitable for enhancing plankton communities and fish production. Water quality within the ponds for the most part was suitable for the rearing of juvenile Murray cod, trout cod and Macquarie perch, as reflected in overall production (growth, survival and yield) from the ponds. However, at times some parameters reached levels which may have stressed fish and reduced growth and survival, in particular, low dissolved oxygen concentrations (minimum 1.18 mg/L), high temperatures (maximum 34°C), high pH (maximum 10.38) and high unionised ammonia (maximum 0.58 mg/L). Species belonging to 37 phytoplankton, 45 zooplankton and 17 chironomid taxa were identified from the ponds during the study. In addition, an extensive checklist of aquatic flora and fauna, recorded from aquaculture ponds in south-eastern Australia, was compiled. However, plankton and benthos samples were usually numerically dominated by a few species only. Rotifers (especially Filinia, Brachionus, Polyarthra, and Asplanchnd), cladocerans (Moina and Daphnid) and copepods (Mesocyclops and Boeckelld) were most abundant and common in the plankton, while chironomids (Chironomus, Polypedilum, and Prodadius) and oligochaetes were most common and abundant in the benthos. Both abundance and species composition of the plankton and macrobenthos varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Chlorophyll a concentrations, which ranged from 1.8 to 184 \ig/L (mean 29.37 ng/L), initially peaked within two weeks of filling and fertilising the ponds. Zooplankton peaked in abundance 2-4 weeks after filling the ponds. The maximum zooplankton density recorded in the ponds was 6,621 ind./L (mean 721 ind./L). Typically, amongst the zooplankton, rotifers were first to develop high densities (2nd-3rd week after filling), followed by cladocerans (2nd-4th week after filling) then copepods (2nd-5th week after filling). Chironomid abundance on average peaked later (during the 5th week after filling). The maximum chironomid density recorded in the ponds was 27,470 ind./m2 (mean 4,379 ind./m2). Length-weight, age-weight and age-length relationships were determined for juvenile Murray cod, trout cod and Macquarie perch reared in ponds. These relationships were most similar for Murray cod and trout cod, which are more closely related phylogenetically and similar morphologically than Macquarie perch. Growth of fish was negatively correlated with both size at stocking and stocking biomass. Stocking density experiments showed that, at higher densities, growth offish was significantly reduced, but survival was not affected. The diets of juvenile Murray cod trout cod and Macquarie perch reared in fry ponds were similar. The cladocerans Moina and Daphnia, adult calanoid and cyclopoid copepods and the chironomids, Chironomus, Polypedilum and Procladius were the most commonly occurring and abundant prey. Selection for rotifers and copepod nauplii was strongly negative for all three species of fish. Size range of prey consumed was positively correlated with fish size for trout cod and Macquarie perch, but not for Murray cod. Diet composition changed as the fish grew. Early after stocking the fish into the ponds, Moina was generally the more common prey consumed, while in latter weeks, copepods and chironomids became more abundant and common in the diet. On a dry weight basis, chironomid larvae were the most important component in the diets of these fish species. Selective feeding by fish on larger planktonic species such as adult copepods and cladocerans, may have influenced the plankton community structure as proposed by the trophic cascade or top -down hypothesis. The proximate composition and energy content of Murray cod, trout cod and Macquarie perch, reared in the ponds did not vary significantly between the species, and few significant changes were observed as the fish grew. These results suggested that the nutrient requirements of these species might not vary over the size range of fish examined. Significant differences in the proximate composition of prey were observed between species, size of species and time of season. The energy content of prey (cladocerans, copepods and chironomids) on a pond basis, was closely related to the abundance of these taxa in the ponds. Data collected from all pond fillings during the present study, along with historical data from pond fillings undertaken prior to this study, were combined in a data matrix and analysed for interactions between pairs of parameters. In particular, interactions between selected water chemistry parameters, zooplankton and chironomid abundance indicators were analysed to identify key factors that influence fish production (growth, survival, condition and yield). Significant correlations were detected between fish production indicators and several water chemistry and biota (zooplankton and chironomids) parameters. However, these were not consistent across all three species of fish. These results indicated that the interactions between water chemistry, biota and fish were complex, and that combinations of these parameters, along with other factors not included in the present study, may influence fish production in these ponds. The present study, showed that more stringent monitoring of fry rearing ponds, especially water quality, zooplankton and benthos communities and fish, combined with an associated increase in understanding of the pond ecosystem, can lead to substantial improvements in pond productivity and associated fish production. In the present study this has resulted in a general increase in fish survival rates, which became less variable or more predictable in nature. The value of such knowledge can provide managers with a more predicative capacity to estimate production of ponds in support of stock enhancement programs and provision of juvenile for aquaculture grow-out.

Can mud (silt and clay) concentration be used to predict soil organic carbon content within seagrass ecosystems?

The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e. silt and clay), however, empirical tests of this theory are lacking for coastal vegetated ecosystems. Here, we compiled data (n = 1345) on the relationship between Corg and mud (i.e. silt and clay, particle sizes <63 μm) contents in seagrass ecosystems (79 cores) and adjacent bare sediments (21 cores) to address whether mud can be used to predict soil Corg content. We also combined these data with the δ13C signatures of the soil Corg to understand the sources of Corg stores. The results showed that mud is positively correlated with soil Corg content only when the contribution of seagrass-derived Corg to the sedimentary Corg pool is relatively low, such as in small and fast growing meadows of the genera Zostera, Halodule and Halophila, and in bare sediments adjacent to seagrass ecosystems. In large and long-living seagrass meadows of the genera Posidonia and Amphibolis there was a lack of, or poor relationship between mud and soil Corg content, related to a higher contribution of seagrass-derived Corg to the sedimentary Corg pool in these meadows. The relative high soil Corg contents with relatively low mud contents (i.e. mud-Corg saturation) together with significant allochthonous inputs of terrestrial organic matter could overall disrupt the correlation expected between soil Corg and mud contents. This study shows that mud (i.e. silt and clay content) is not a universal proxy for blue carbon content in seagrass ecosystems, and therefore should not be applied generally across all seagrass habitats. Mud content can only be used as a proxy to estimate soil Corg content for scaling up purposes when opportunistic and/or low biomass seagrass species (i.e. Zostera, Halodule and Halophila) are present (explaining 34 to 91% of variability), and in bare sediments (explaining 78% of the variability).