Environmental magnetic methods for detecting and mapping contaminated sediments in lakes
The remediation of contaminated sediments is an urgent environmental priority in the Great Lakes and requires detailed mapping of impacted sediment layer thickness, areal distribution and pollutant levels. Magnetic property measurements of sediment cores from two heavily polluted basins in Lake Ontario (Hamilton Harbour, Frenchman's Bay) show that concentrations of hydrocarbons (PAH) and a number of heavy metals (Pb, As, Ni, Cu, Cr, Zn, Cd, Fe) are strongly correlated with magnetic susceptibility. The magnetic susceptibility contrast between the contaminated sediment and underlying 'pre-colonial' sediments is sufficient to generate a total field anomaly (ca. 2-20 nT) that can be measured with a magnetometer towed above the lake bed. Systematic magnetic surveying (550 line km) of Hamilton Harbour using a towed marine magnetometer clearly identifies a number of well-defined magnetic anomalies that coincide with known accumulations of contaminated lake sediment. When calibrated against in-situ magnetic property measurements, the modeled apparent susceptibility from magnetic survey results can be used to classify the relative contaminant impact levels. The results demonstrate the potential of magnetic property measurements for rapid reconnaissance mapping of large areas of bottom contamination prior to detailed coring and sediment remediation.
Correlating Magnetic Properties and Heavy Metal Content in Sanitary Leachate Sludge: A Case Study from Bandung Indonesia
In this work, we obtained landfill leachate sludge samples from two municipal solid waste disposal sites (Jelekong and Sarimukti) near Bandung, West Java, Indonesia and measured their magnetic properties and heavy metal content. The objective is to test whether there is a correlation between magnetic properties and heavy metal content that would allow the use of magnetic properties as proxy parameters for heavy metal content. The leachate was found to be sufficiently magnetic with mass-specific magnetic susceptibility that averaging 262.09 x 10-8 m3 kg-1 for Jelekong and 155.29 x 10-8 m3 kg-1 for Sarimukti, In both sites the magnetic minerals are predominantly pseudo-single domain (PSD) magnetite. Leachate samples from the older but inactive disposal site, Jelekong, are found to be more magnetic than that from, Sarimukti, the younger and active site. The enhancement of leachate due to the soil-derived ferrimagnetic particles is possibly the same for both Sarimukti and Jelekong. Based on AAS analyses, leachate samples from Jelekong were found to have higher heavy metal content than that from Sarimukti. Higher concentrations of heavy metals at Jelekong could be caused simply by the accumulation of heavy metal over prolonged period of time. The low frequency magnetic susceptibility correlates well with almost all heavy metals, with the exception of Cr, As, and Pb. These correlations suggested that the heavy metals have strong affinity with the ferrimagnetic minerals. Moreover, they also suggested that both heavy metals and ferrimagnetic minerals share the same origin, i.e., the waste instead of the soil. In contrast, the correlations between magnetic parameters and heavy metals in leachate samples from Sarimukti are much poorer. The fact that strong correlation between magnetic parameters and heavy metals is observed in Jelekong but is absent in Sarimukti suggests that the use of magnetic measurement as a proxy measurement for heavy metal content in leachate is plausible provided that the magnetic susceptibility exceeds certain threshold value. Moreover, the accumulation of magnetic minerals and heavy metals in leachate might depend on the activity and the age of landfill sites.
Relationship Between Physical Properties and Magnetism of Soils From Various Pedoenvironments
Characterization of soils with respect to their fertility, sustainable use and conservation require extensive, time- consuming and costly analyses. Establishment of well defined relationships between certain physical, geochemical and magnetic parameters would be useful tool in pedometrics, giving opportunity to carry out large scale studies on soil properties in more economically effective and fast way. Interdisciplinary analysis of 15 type soils from different pedoenvironments (oxidative, water-logged, salty, etc.) includes extensive magnetic measurements (magnetic susceptibility, anhysteretic (ARM) and isothermal (IRM) remanences, hysteresis parameters); determination of a set of physical characteristics (grain size fractions, pH) and geochemical analyses (total Fe content, oxalate- and dithionite-soluble Fe). Empirical linear relationship is found between soil reaction (pH) and magnetic susceptibility for aerobic soils, and negative relationship between pH and ARM for water-logged soils. Different type soils, showing magnetic enhancement along the solum, show higher ARM intensity with increasing percent of the clay fraction. This feature most probably is related to the fact that pedogenic ferrimagnetic minerals are strongly linked to clay fraction. The absence of such correlation for soils, affected by water-logging conditions suggests prevailing role of amorphous phases and antiferromagnetic Fe oxides in magnetic mineralogy. The role of pedogenic factors for particular behavior of other magnetic parameters will be discussed.
Effects of Atmospheric Pollutants on Plant Growth and on Soil Magnetic Properties: Preliminary Results from Controlled Experiments
The effects of an iron pollutant (magnetite, <5µm) on both tomato plants and their growth media (soil) in garden pots have been examined in this study. Morphological differences in the plants subjected to different concentrations (0.04 mg/kg and 0.4mg/kg) of the pollutant have been monitored at different ontogenic stages by measuring plant height and leaf colour, using a reflectance spectrometer (USB 4000). The surface magnetic susceptibility (MS) of the growth media has been measured using the Bartington MS2 system on a weekly basis. The changes in soil magnetic properties and some trace element concentrations of elements potentially associated with Fe have been determined through magnetic and chemical methods. The preliminary results in the control samples and a few of the contaminated samples show that exposure to iron contaminant can affect plant growth significantly, and can change the magnetic susceptibility of the growth media. Distinct morphological differences are observed in plants subjected to different treatments. The control plants are much taller (30-40cm, measured to date) compared to low-contamination (20-30cm) and high- contamination plants (10-15cm). In contrast, the mean brightness and saturation values of the leaves did not vary substantially. These colour parameters were hypothesized to vary significantly; however an explanation for their similarity is still being researched. The average decrease in MS is about 23% in the control soil. From a theoretical perspective, with the decrease in MS, there should be a corresponding decrease in iron minerals, which should be observable by chemical methods. However the MS values increased in most of the samples with contaminated soils but the mechanism by which this occurs is unclear. We would expect that, in such a controlled environment, any changes in soil magnetic properties and trace element concentrations must be due to the plant growth and its effects on the surrounding soil. The background values of the trace element concentration investigated by AAS show that Pb is below detection limit; Mn is between 2-7 ppm while Zn is below 1ppm. Fe, however is 40 ppm in the control soils and is between 42-160 ppm in contaminated soils. Such low concentrations of Fe could be due to incomplete digestion during sample preparation. Trace element concentrations in soils and in fully grown plants will be examined, from which the concentrations of the trace elements consumed by plants will be inferred. To better understand the effects of the contaminant on plant growth and on soil magnetic characteristics, additional experiments are recommended. It is anticipated that this research will help to improve our understanding about pollution distribution dynamics through the assessment and evaluation of known anthropogenic pollutants in controlled experiments.
Particle Size Specific Magnetic Fingerprinting of Beach Sands: Point Pelee National Park, Ontario, Canada.
Point Pelee National Park, located on the northern shore of Lake Erie, is a classic example of a cuspate sand spit and contains a UNESCO protected wetland, which provides habitats for a wide range of protected and rare species. However, its existence is threatened by increasingly frequent breaches of the narrow east barrier beach that separates forest and wetlands from the greater Lake Erie basin. Robust identification of sediment sources and understanding of beach sediment dynamics is therefore critical for the effective deployment of measures aimed at reducing these risks and is especially critical given future climate projections of greater storm frequency and intensity. Here we magnetically fingerprint beach sediments with a view for comparison with potential sources in order better target mitigation measures. In situ magnetic susceptibility ranges from 4 - 30,000 10-6 SI along the beach with swash zone sediments clastically coarser and magnetically weaker than the 'back beach' sediments illustrating the heterogeneity in the distribution of magnetic minerals. Vegetation type appears to have a local effect on the distribution of magnetic susceptibility, with samples bordering the Carolinian forest often several orders of magnitude greater than those bordering the marsh. Magnetic properties are highly particle size dependent, with the particle size fractions 250-125 um and < 125 um contributing 3-4 x more to the bulk magnetic signal than would be expected from the clastic (physical) grain size distributions making particle size specific measurements essential. High susceptibility values and steep remanence acquisition indicates dominance of ferrimagnetic minerals and whilst the beach sands are dominated by a coarse grained magnetite-like signal, the > 1000 and < 250 um fractions display significant differences between the magnetic properties of the swash zone and vegetation bordering sands indicating particle transport and sourcing differences. Comparison of representative sample fractions from the east beach to sands from the western beach and eastern potential source areas can help identify principal source areas, explain and clarify sedimentary processes and regimes and develop mitigation strategies aimed at sustaining this fragile wetland ecosystem.
Evaluation And Application Of Biomagnetic Monitoring Of Traffic-Derived Particulate Pollution.
Inhalation of particulate pollutants below 10 micrometres in size (PM10) is associated with adverse health effects. Here we examine the utility of magnetic remanence measurements of roadside tree leaves as a quantitative proxy for vehicle-derived PM, by comparing leaf magnetic remanences with the magnetic properties, particulate mass and particulate concentration of co-located pumped air samples (around Lancaster, UK). Leaf samples were collected in early autumn 2007 from sites in close proximity to a major ring road, with a few additionally from background and suburban areas. Leaves were collected from lime trees (Tilia platyphyllos) only, to avoid possible species-dependent differences in PM collection. Magnetic susceptibility values were small and negative, reflecting the diamagnetic nature of the leaves. Low- temperature remanence curves show significant falls in remanence between 114 and 127 K in all of the leaf samples. ×ARM/SIRM ratios indicate that the dominant size of the leaf magnetic particles is between c.0.1-1 micrometre. Analysis of leaf particles by SEM confirms that their dominant grain size is less than 1 micrometre, with a significant number of iron-rich spherules less than 0.1 micrometre in diameter. Particle loading is concentrated around ridges in the leaf surface; significant numbers of the finer particles (less than 500 nm) are frequently agglomerated, most likely due to magnetic interactions between particles. Larger particles exhibit an irregular morphology, with high silica and aluminum content. Particle composition is consistent with exhaust outputs collected on a filter. Critically, leaf SIRM values exhibit strong correlation with the particulate mass and SIRM of co-located, pumped air samples, indicating that leaf SIRMs are an effective proxy for ambient particulate concentrations. Biomagnetic monitoring using tree leaves can thus potentially provide high spatial resolution data sets for assessment of particulate pollution loadings at pedestrian-relevant heights. Not only do leaf SIRM values increase with proximity to roads with higher traffic volumes, leaf SIRM values are c. 100 % higher at 0.3 m than at c. 1.5 to 2 m height.
Magnetic Monitoring In Urban Soils From Merida, Yucatan Mexico.
We studied urban soils samples from Merida Yucatan Mexico using magnetic methods. Measurements of magnetic susceptibility (X) at high and low frequencies allowed us to obtain Xfd, whose values indicate a high SP grains content in most samples. We calculated S-200 and S-20 ratios from IRM measurements. These parameters are the Isothermal remanent magnetizations at -200 mT and -20 mT (back-field IRM) normalized to saturation values (IRM-200/SIRM and IRM-20/SIRM). Most of the samples contain ferromagnetic minerals as magnetic carriers since S-200 values are between 0.8 and 1.0. Also, the SIRM/X ratio has a great correlation with metal content: Pb and Zn, principally.