The population of coloured fibres in human head hair

A trace fiber population study on upholstered chairs in a military environment

This fiber population study has assessed the prevalence of the color and type of trace fibers present on upholstered seats in a specific setting to identify the most common and rare colors and to determine their evidentiary value. Nearly 22,000 fibers were collected via tape lifts from 25 fabric covered chair seats in a lobby area on Beale Air Force Base and examined microscopically to determine their apparent colors. Overall, blue and white/colorless were the most and nearly equally common colors (32.0 % and 31.5 %, respectively), followed by black/grey (19.6 %), brown (8.6 %), yellow/tan (4.9 %), and red/pink (2.5 %), while orange, purple, and green were the rarest (0.5 %, 0.3 %, and 0.3 %, respectively). Among rarest color fibers, plant-based fibers were predominant (77.7 %), consisting of mainly cotton, followed by synthetic fibers (17.4 %), then the least prevalent animal fibers (5.0 %). These color rankings align similarly to previous studies, despite the prominence of blue color fibers and higher proportions of brown and yellow/tan color fibers.

Fibres in the nasal cavity: A pilot study of the recovery, background, and transfer in smothering scenarios

In cases where the suspected cause of death is smothering, fibre traces recovered from the nasal cavity are hypothesised to refute or support this proposition. In order to carry out such evaluations, an efficient recovery method must first be established. This pilot study tested five different recovery methods on 3D printed models of nasal cavities. Among which, the use of the transparent AccuTrans® polyvinyl Siloxane casts demonstrated the best recovery efficiency with a median of 90% of deposited fibres recovered. The efficacy of this method was then verified on cadavers. Apart from a reliable recovery method, an understanding of the background population of fibres in nasal cavities, as well as the mechanisms of the transfer from the purported smothering textile to the nasal cavity is essential to evaluate the findings in these cases of suspected smothering. Samplings of the nasal cavities of 20 cadavers were thus carried out to gather data on the background population of fibres. Results showed that nasal cavities are not void of fibres, but the quantities are expected to be low, with a mean of 3.8 fibres per cavity recovered. Information on generic fibre class, colour, and length of these background fibres were also obtained with the use of low and high-power microscopy. The frequencies found in this population of fibres closely align with data from other population studies where black cotton was the most common. Finally, transfer experiments using the 3D printed models fitted with a respiratory pump to simulate breathing were carried out, along with testing on live volunteers in-vivo. The results demonstrated a verifiable transfer of fibres into the nasal cavity in smothering scenarios. Textiles of various shedding capacities were used in these tests and the findings suggest an influence of this variable on the quantities of fibres transferred.

The transfer of fibres between garments in a choreographed assault scenario

Our fundamental understanding of fibre transfer remains based on early seminal transfer studies that were largely mechanical simulations. However, transfer events in the real world are uncontrolled in nature. This study takes a novel approach to address this discrepancy, with skilled jiu-jitsu practitioners performing a choreographed 'standard' assault scenario to investigate the transfer of fibres between a cotton T-shirt and cotton/polyester hoody. Garments were collected immediately after the scenario and examined for the number, length and zonal distribution of transferred fibres. It was observed that cotton transferred the most fibres, on average twice as many from blended hoodies than T-shirts; whilst polyester transferred the least. Shorter fibres transferred and were recovered more readily than longer fibres; however, it was more likely to recover polyester fibres> 5 mm. The number and length of fibres transferred from the attacker's garment mainly depended on the construction of the donor textile (including sheddability) and properties of the fibres. Conversely, properties of the recipient textile were more significant factors when considering transfer from the victim's garment. Location of recovered fibres was found to be dependent on the wearer's role, but generally, upper zones and sleeves of both garments were most populated. Overall, these results will contribute to grow our current knowledge base regarding fibre transfer between donor and recipient textiles in a common assault situation. This will ultimately aid experts support evaluation with regards to competing hypotheses such as in a Bayesian framework.

Prevalence and characterisation of microfibres along the Kenyan and Tanzanian coast

Microplastic pollution is ubiquitous, with textiles being a major source of one of the dominant microplastic types—microfibres. Microfibres have been discovered in the aquatic environment and marine biota, demonstrating direct infiltration in the environment. However, the impact of non-plastic microfibres has been overlooked until recently despite their prevalence and the ecotoxicological risk posed by chemical dyes and finishes used during processing. During an expedition from Lamu to Zanzibar (East Africa), a citizen science strategy was employed to innovate, educate and influence microfibre pollution reform through the Flipflopi project, a circular economy effort to stop the use of single-use plastic. Simple sampling methods were developed to replace costly equipment, which local citizens could use to partake in the collection and sampling of surface water samples from the previously understudied Kenyan and Tanzanian coast. To maintain the reliability of samples and to minimise contamination, a forensic science strategy was embedded throughout the methodology of the study, collection and analysis of the samples. A total of 2,403 microfibres from 37 sites were recovered and fully characterised with 55% found to be of natural origin, 8% regenerated cellulosic and 37% synthetic microfibres. Natural microfibres were in higher abundance in 33 of the 37 sampled sites. Congruent with recent studies, these findings further support the need for greater understanding of the anthropogenic impact of natural microfibres.

A population study of textile fibres on the seats at three public venues

A population study was carried out by collecting textile fibres present on the seats in a church, a cinema and a conference centre in Linköping, Sweden. The collection was carried out in such a way as to avoid inadvertent fibre collectives and to enable comparison of the frequency data between venues. In total 4220 fibres were examined and details of their characteristics were recorded and entered into a searchable database. Only coloured fibres over 0.5 mm in length were included in the study. 70% of the fibres were classified as cotton, 18% were man-made, 8% wool, 3% other plant and 2% other animal. Polyester and regenerated cellulose were the most abundant man-made fibres. The most frequently occurring combinations were blue and grey/black cotton, making up approximately 50% of all fibres. All other combinations were made up of less than 8% of the fibres, with red cotton being the next most prevalent. The results regarding the most frequently occurring fibre types, colours and colour/fibre type combinations are comparable to those of other population studies that have been carried out in different countries over the last 20-30 years. Additional observations regarding the frequency occurrence of certain characteristics are presented, such as differences in thickness, cross-sectional shape and presence of pigment or delustrant for the man-made fibre types.

The transfer of fibres via weapons from garments

Stabbings have been reported as the most frequent violent crime in countries where there is a severe restriction on obtaining firearms, such as the United Kingdom. Knives, scissors, and screwdrivers, as studied in this research, are among the most commonly encountered weapons involving stabbing events. When any of these implements are used in a stabbing, there is potential for the garment(s) worn by the victim to be damaged. In such an instance, there is an opportunity for fibres to be transferred to the weapon used, thus providing forensic evidence of proof of transfer from the victim's clothing to the weapon. This can offer valuable information in establishing what weapon was used to harm the victim through linking fibres from the victim's garment(s) to a weapon recovered from a suspect. This research simulates vertical stabbings - performed by a human participant - in to a polystyrene block supporting the clothing (essentially acting as the victim's torso), to reflect an authentic scenario. The aforementioned weapons were used along with 3 varieties of garments (cotton, polyester and a linen/viscose mix) offering different characteristics of shedability and structure for the simulated stabbings. Low power microscopy was utilised to view the transferred fibres. The amount of fibres transferred on to the implement were recorded for each repeat. 2279 individual fibres were found over 10 repeats from the knife in relation to the linen/viscose garment. This was the highest amount of transference found with the lowest number attributed to the screwdriver-polyester relationship, providing 320 recorded fibres over 10 repeats. The findings of this study suggest that the number of fibres transferred is not only related to the shedability of the garment but also the surface area characteristics of the receiving weapon and the ability for the garment to tear.

Freshwater and airborne textile fibre populations are dominated by 'natural', not microplastic, fibres

The potential role of natural textile fibres as environmental pollutants has been speculated upon by some environmental scientists, however, there is a general consensus that their biodegradability reduces their environmental threat. Whilst the risks that they pose remain poorly understood, their environmental prevalence has been noted in several recent microplastic pollution manuscripts. Here we highlight the extent to which natural textile fibres dominate fibre populations of upstream reaches of the River Trent, UK, as well as the atmospheric deposition within its catchment, over a twelve month microplastic sampling campaign. Across 223 samples, natural textile fibres represented 93.8% of the textile fibre population quantified. Moreover, though microplastic particles including synthetic fibres are known to be pervasive environmental pollutants, extruded textile fibres were absent from 82.8% of samples. Natural textile fibres were absent from just 9.7% of samples.

A study of background population of fibres on knife blades

Edged weapons are frequently used to commit violent crimes (e.g., homicides, assaults or sequestrations). Following a stabbing, a fibre transfer might occur from the damaged fabric to the blade. It is crucial to investigate whether the target fibres were transferred to the blade as a result of the stabbing and if they are in association with the offence or whether they originate from another unrelated event (i.e., part of the background). The aim of this study is to explore the background population of fibres recovered on knife blades (police seizures and everyday knives) to help the interpretation of the results stemming from the analysis of the fibre evidence in crime cases involving the use of a bladed weapon. A population study was carried out to learn about the variety, the distribution and the size of the fibre population present on knife blades. After recovery using tapes lifting, stereoscopic examinations were performed to classify around 1500 fibres according to their colour and generic type. The most common colour/type combinations were: colourless/white cotton (31%), blue cotton (16%) and grey cotton fibres (11%). As blue fibres represent one of the most common colour group, they were selected to carry out a colour block study (based on microscopy observations and microspectrophotometry UV-vis spectra) to investigate the number and the size of the groups of indistinguishable fibres present on each blade. Only 30% of the knife blades presented more than one blue cotton fibre. The number of groups found per knife varied between 1 and 3, each group containing between 2 and 6 fibres. Findings revealed an important difference between the background fibre populations in terms of quantity of fibres, their morphology and spatial distributions - and the population of fibres transferred in a stabbing. The collected data can be used in a Bayesian approach to help with the interpretation of results.

An investigation into the persistence of textile fibres on buried carcasses

A significant amount of research has been carried out on fibres to aid the forensic scientist in determining the significance of these when found on a victim or suspect. This work has focused on open-air environments, and as such no research has been undertaken to examine the persistence of fibres on bodies in the burial environment. Wool and cotton fibres, known to fluoresce under ultraviolet (UV) light, were transferred onto the skin of four porcine (Sus scrofa) carcasses (two carcasses per fibre type). The number of fibres transferred was recorded from images taken under UV light. The remains were subsequently placed in four burial sites and left interred for 14 days. After this period the carcasses were excavated and lightly brushed down to remove the soil layer that had adhered to the skin. Once again photography under UV light was used to record the number of fibres which persisted on the skin. Results showed that after 14 days, wool and cotton fibres remain on the surface of the buried carcasses. In no circumstance was there a total loss of fibres suggesting that in such scenarios, the likelihood of finding fibres is high but the initial number of fibres transferred would be strongly diminished. This has important implications for both the excavation protocol for buried remains and the subsequent analysis for physical evidence.

The secondary transfer of fibres from head hair

In this study, the effects of fibre type, hair style, time and fibre persistence on the secondary transfer of mask fibres to pillowcases via head hair were studied. Volunteers with a range of hair styles, and masks consisting of different fibre compositions were used in the study. Fibres from the masks were found to transfer from donor subjects to the pillowcases up to 14 nights after the mask had been worn. On average, the number of secondarily transferred fibres found decreased with time; however, this decrease appeared to be more 'linear' in nature, rather than an exponential decay. The greatest degree of secondary transfer occurred with cotton, then acrylic, then wool. In a primary transfer/persistence experiment with a 50% acrylic/50% wool mask, wool was found to persist in the hair more readily than acrylic. The results also showed that the greatest degree of secondary transfer occurred via short straight and long straight hair, with no clear pattern emerging between medium length hair (both straight and curly) and with long curly hair. The implications of these findings for the assessment and interpretation of casework are considered along with data obtained from related studies.

The population of coloured textile fibres in domestic washing machines

A population survey was carried out to analyse examples of the coloured fibre population that may be expected to exist in both front- and top-loading domestic washing machines during Spring, in Sydney, Australia. White cotton T-shirts were washed both individually, and with a normal household wash load, then taped to recover extraneous fibres transferred during the wash cycle. Twelve thousand one hundred and seventy-eight fibres were classified according to length, colour and generic class. Cotton fibres were most prevalent (69.4%), followed by man-made fibres (24.2%). The most common colour/generic class combinations were black/grey cotton (27%), blue cotton (20%) and red cotton (15.6%). Other combinations generally represented under 2% of the total fibre population. Two thirds (65.9%) of the recovered fibres were under 2 mm in length, the proportion of fibres decreasing with increasing fibre length. Variations in machine type did not affect the distribution of fibres with respect to fibre type, colour or length.

A target glitter study

A target study was conducted using four different pre-selected types of commercial glitter particles. Recipient areas in the general environment around San Diego, California were tested. Glitter particles were recovered using double-sided tape affixed to square plastic Petri dishes. White light microscopy was the only search/identification method used. Additionally, a test was performed of the transferability of cosmetic glitter. Glitter particles were found to readily transfer. Of a total of 48 tape lifts from the general environment, 23 were found to contain at least one glitter particle. But due to the wide variety of glitter particles in terms of colour, shape, size, and surface morphology, the likelihood of transfer of one or more specific target particles was small.

Advances in chemistry applied to forensic science

Acts of terrorism, an increase in the use of firearms, drug abuse, the use of so-called date-rape drugs, and driving whilst under the influence of drugs, are just some of the subjects frequently in the news. In the absence of fingermarks and of material leading to the recovery of DNA, the forensic scientist has to rely upon chemical analysis of trace amounts of materials including explosives, drugs, toxicological specimens, firearms discharge residues, fibres, glass, paint, soil etc., in order to establish or eliminate links between suspect and victim and/or scene. This tutorial review describes analytical problems facing the forensic chemist, and the current methods and techniques employed to tackle them.