Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment (Soil Taxonomy, USDA)
The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants.
The lower boundary that separates soil from the nonsoil underneath is most difficult to define (Soil Taxonomy, USDA). Soil consists of horizons near the Earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification,
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the lower boundary of soil is arbitrarily set at 200 cm hence the name soil taxonomy.
Forensic analysis of soils or better known as forensic geology is the study of evidence in relation to the crime that in need in the court of law in term of minerals, soil, petroleum and other materials found in the Earth. The value that lies in the almost unlimited number of kinds of materials in soil is tremendous. Large numbers of measurement and observation can be done to rocks, minerals, soils and related materials due to their evidential value. For example, the number of particle sizes and distributions of grains combined with colours, shapes and mineralogy are almost unlimited. These properties are identifiable, recognizable, and can be characterized. It is this diversity in earth materials, combined with the ability to measure and observes the different kinds, provides the forensic discriminating power.
There have been many contributions to this discipline of forensic soil analysis over the last 100 years. Many researches have been made by the Laboratory of the Federal Bureau of Investigation, in Washington D C., McCrone Associates in Chicago, The Centre for Forensic Sciences in Toronto, Microtrace in Elgin, Illinois, the former Central Research Establishment at Aldermaston, Kenneth Pye Associates Ltd in Great Britain, The Japanese National Research Institute of Police Science, The Netherlands Forensic Institute-naming among few of famous soil forensic laboratories in the world.
Because much of the evidential value of earth materials lies in the diversity and the differences in the minerals and particles of soil, microscopic examination at all levels of instrumentation is the most powerful tool. In addition, such examination provides an opportunity to search for man-made artefact grains and other kinds of physical evidence.
1.2 Objective of study
The study is prior to these purposes:
i) To understand the taxonomy of the local soils. Soil taxonomy is a method is soil classification based on its composition as the key feature.
ii) To identify the factors or soil properties that can affect the decomposition rate.
iii) To observe, measure and indicate how the factors that has been identified, can affect the decomposition rate.
Significant of study
Diversity in soils chemical and physical properties lead to delinearity of decomposition rate. The fact affecting the rate of organic matter decomposition- which is the interest of this study, in different soil types will be studied. Soils as diverse as it is contain a lot of existing microbes, biological organism and chemical composition which is unique to each type of it, that involve in decomposition process (Patrick et al., 1993). Understanding the soils variety can help to understand the role it plays in decomposition process and help in interpreting the time interval of death of dead body in crime cases. Due to the difference in soil properties which can give rise to different rate of decomposition, and by understanding the relation, interpreting the death interval at more accurate time range can be endorsed.
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Soils may constitute evidence that connects a person or object to a particular location. The value of soil stems from its ubiquity and transferability to objects or persons. Due to the complexity of soil, the analysis of its inorganic and organic components can provide complementary and independent types of information about its geological origin, dominant vegetation, management and environment. An overview of a range of soil characterisation methods including chemical analysis, mineralogy and palynology, along with new approaches such as DNA profiling (Reza et al.,2010) and profiling of other digital data such as that obtained from X-ray powder diffraction, infrared spectroscopy (Gavaraglia, 2000; R.Linker et al., 2009) and organic marker analysis were reviewed extensively lately for its value in forensic investigation.
Decomposition in terrestrial ecosystem are determined by a set of regulars factors which regulate microbial activity at decreasing scale of time and space in the order of: climate-clay mineralogy, nutrient status of the soil-quality of decomposing resources and effect of microorganisms (i.e., roots and invertebrates) (Patrick, et al.,1993). In humid country as Malaysia due to proximity waters with average temperature at 20-30°C, decomposition can be altered henceforth the estimation of the time of death. It is well understood that temperature can have significant effect on the decomposition of cadaver due to metabolism of microbes and soil chemical reaction (Paul et al., 1996). Furthermore, varsities in soils type give rise to different set of bacterial ecology in the soil environment. Soil with an active microbial population may have the capacity to decompose organic matter more quickly (Fiedler and Graw 2003) and soils exposed to cadavers (or potentially simply fertilisation with NH4) previously, may have a community of bacteria and fungi adapted to cadaver decomposition (Carter and Tibbett 2008).
This extrinsic factor aside from burial depth of cadaver and insect access regulate the mutual relationship of macro-microorganism ultimately the rates and pathways of decomposition (Kenneth et al., 2005). Physical texture, whether the soil is sandy, silty or clayey can profoundly affect the rate of decomposition by limiting the movement of gasses and water to and from the site of biodegradation and O2 demand and waste gas generation (i.e. the cadaver). On the other hand, the acidity, alkalinity, nutrients and level of contamination of a soil may affect decomposition rates profoundly (Tamsin et al., 2009).
2.2 Forensic value of soil
Comparison of soil physical has helped to solve many crime cases. The comparison based on soil particle, color, and composition of clay, sand and many more has help justice to be served. Current analytical methods allow forensic scientists to either concludes that the evidence did not share a common source with a standard or that the two soil types are similar in all analytical respects and cannot be excluded (Cox et al.,2000). However, decomposition of dead body-cadaver as far as this study concerned has poorly understood. This is the area of forensic taphonomy which aims to provide information relevant to the courts in cases where cadavers have been allowed to decompose. The studies of the effects of the local soil composition towards decomposition process were not many reviewed although has been extensively reviewed in many abroad literatures.
Post mortem interval (PMI) is the time elapses since a person has died. Determination of PMI commonly done by the pathologist by looking at several common factors such as algor mortis, rigor mortis, vitreous humour, autolysis and forensic entomology. According to Jaggers et al., soil moisture has a significant impact on type, rate and the extent of body degradation which ultimately affects estimations of PMI. The influence of moisture on decomposition in soil is generally due to its effect on soil microbial activity, as microorganisms are the primary decomposers in soils (David, et al.,2010). Modification of soil composition can also alter the estimation of PMI.
3.1 Soil Sample
The soil samples for this study will be taken in the area of Skudai,Johor. The differentiation of each sample will be characterized via United States of America Soil Taxonomy. The selected soils are Brown Sodosol which has loamy sand texture, Rudosol that has sandy texture and Grey Vertisol that has medium clay texture (David et al., 2010). Pre-treatment of the soil will be performed accordingly to the Method for Soil Analysis, USDA revised version 2006.
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Juvenile rat (Rattus rattus) cadavers (18g wet weight) aged 8-10 days were used as organic resource patches. Rats were killed with carbon dioxide immediately prior to burial (David et al.,2008).
3.3 Experimental Design
The soil samples will be sieved to a similar particulate size. The weight of each soil samples will be constant at 500g after incubation at 22°C (Carter et al., 2008). The measurement of cadaver decomposition will be done according to cadaver mass loss (Carter et al., 2008), soil pH (Veronique., 2006), microbial biomass carbon (Anderson and Domsch., 1978), and enzyme activity (Ladd and Butler, 1972).
3.3.1 Cadaver Mass Loss
Upon exhumation, cadavers will be immediately frozen (-20°C). Once frozen the cadavers were rinsed with distilled water to remove any additional soil, dried with a paper towel and weighed.
3.3.2 Soil pH
The pH of the soil will potentiometrically measured in the supernatant suspension of a 1:5 soil: liquid (v/v) mixture. This liquid is a 0.01 mol/l solution of calcium chloride in water pH-CaCl2 or water pH-H2O. A representative sample (at least a volume of 5 ml) of the air-dried soil (fraction < 2 mm) will be taken. The test sample will be placed in the sample bottle and calcium chloride solution (pH-CaCl2) or water (pH-H2O) will be added five times of the test sample's volume. The suspension will be shook and mixed vigorously for 5 minutes before let to be stabled for 2 hour. The measurement of suspension's temperature will be taken and ensured not to be differentiating more than 1°C from the pH meter buffer solution. (Veronique, 2006).
3.3.3 Carbon Dioxide Evolution
30 ml vial (Crown Scientific, Newstead, Queensland, Australia; Product no. 735) (CO2 trap) will be filled with 20 ml sodium hydroxide (NaOH) (0.465 M) and suspended above the soil surface inside incubation chambers designated for soil sampling after 28 days. The incubation chamber will then be sealed. CO2 traps and the air in the incubation chamber headspace need to be replaced every 24 hour. Upon removal from the incubation chamber the electrical conductivity of the NaOH solution inside the CO2 trap will be measured using a Metrohm 660 Conductometer (Herisau, Switzerland) (Rodella., 1999)
3.3.4 Microbial Biomass Carbon
Microbial biomass carbon can be estimated within 1 hour of harvest using the substrate-induced respiration (SIR) technique (Anderson and Domsch, 1978) with some modifications (Lin and Brookes, 1999). Soil (5 g dry weight) will be weighed into 30 ml McCartney bottles and amended with glucose solution (6 mg/ g soil) in order to calibrate them to 95%water-holding capacity. Following the amendment on the glucose solution, a 6 ml vial containing 5 ml NaOH (0.1 M) (CO2 trap) will be placed on the soil surface and the McCartney bottle was immediately sealed. Samples will then incubate in the dark at 22°C for 3 or 4 hours based on preliminary experiments. After the incubation period CO2 traps were then removed and sealed. The NaOH solution from the CO2 traps was backtitrated with HCl (0.1 M) into 5 ml BaCl2 (1.0 M) and 3 drops phenolphthalein as indicator (Rowell, 1994 and Davie et al.,). Microbial biomass carbon was then calculated as in Anderson and Domsch, 1978.
3.3.5 Enzym Activity
The activity of casein-hydrolysing protease and phosphodiesterase (orthophosphodiester phosphohydrolase: EC 126.96.36.199) will be assayed. Proteolytic hydrolysis of casein will be measured as describe in detail in Ladd and Butler (1972). The procedural involved the usage of protein and dipeptide substrate in the absence of added bacteriostatic agents. The rate of substrate hydrolysis was proportional to the soil concentration; the release of amino compounds per unit weight of soil was directly related to the incubation time.
4.1 Soil Sample
Johor encompass about 27% of overall peat soil distribution in Malaysia (Soil Map Malaysia, 2004). This study expects to observe major peat soil characteristic during physical and chemical characterization of soil samples taken around this state area. Though, the major area are covered with peat soils, organic soil The variance in soil properties which will be expected to be discovered are in term of soil pH, bulk density, water conductivity, leeching ability, colours and total organic content.
4.2 Experimental Result
Decomposition rate in collected sample soils are expected to will be different. Soils with low pH value and low water conductivity proposely will expect to give high rate of decomposition. Soil with high sand, clay and silt composition however, is predictedtoexpected to give low rate of decomposition due to high aeration and high water conductivity. The relation in between factors involve in decomposition among the soils will be made through similar pattern revealed during the study.
The study hopes to achieve all of its objectives. The taxonomy of locally collected soil sample will be understood through detailedthorough study and classification. The factors involve in decomposition and the properties soil factors that are giving impact in the process will be also identified. Understanding the unique characteristic of soil will help in understanding the nature way in differentiating the cycle of decomposition of organic material which. It is beyond what a the naked eye can see. Knowledge relating the nature cycling of organic matter and pathology determination of time of death in lab will help forensic scientist pronouncing the right of a casualty in a more assertive way.