Bacteria, guano and soot: Source assessment of organic matter preserved in black laminae in stalagmites from caves of the Sierra de Atapuerca (N Spain)

Speleothems are a recognized source of paleoclimatic information, but their value as a source of signals from human activities in caves with an archaeological record has rarely been explored. Previous studies of speleothems in the Sierra de Atapuerca karst system (Burgos, northern Spain) revealed an important human fossil record, provided information about human activities in and around these caves, and the impacts on their natural environment. The present study reports the results of molecular characterization of dark-colored laminae from the stalagmites Ilargi (Galería de las Estatuas) and GS1, GS2, and GS3 (Galería del Silo), by pyrolysis-GC-MS (Py-GC-MS) and thermally assisted hydrolysis and methylation (THM-GC-MS). The features of the organic matter demonstrate the presence of (1) a dominant aliphatic fraction probably from in situ bacterial and ex situ plant-derived lipids, (2) black carbon (from soot and/or charcoal), (3) polysaccharides and N-rich moieties (probably from bat guano and microbial sources), and (4) a signal of terpenoid derivatives that may originate from the overlying limestone (kerogen) and extant gymnosperm resin (soils) or cyanobacteria (cave). Some plant-derived lignin may be present as well but was not identified unambiguously. It is concluded that this approach allows identifying multiple general sources of organic matter which can help understand speleothem formation processes, and evidence of soot deposition could be clearly linked to human activities.

Optimization of soot deposition by high-temperature prepolarization of a resistive particulate matter sensor

For the purposes of the onboard diagnosis (OBD) of diesel particulate filters (DPFs) in diesel exhaust treatment systems, a particulate matter (PM) sensor is applied downstream from the DPFs to detect small amounts of diesel soot that passed through the filter. The state-of-the-art technology is a sensor based on the resistive measurement principle, i.e., charged soot particles are attracted by electrophoretic forces, deposited on an interdigital electrode (IDE) structure and conductive soot bridges that reduce the overall resistance are formed. This paper reports how the response time of a resistively working particulate matter sensor can be shortened up to 30 % by the optimization of soot deposition that is initiated by a change in the sensor operation strategy. The measurement voltage is applied for prepolarization during the sensor regeneration phase rather than during the cooling phase before the measurement is commonly done. Experiments were performed at diesel engine test benches to examine this context and simulations of the electric field above and below the IDE structure. The data are used to deduct a model, including the solid state chemistry of the sensor's ceramic materials, the effect of impurities on the electric field properties and the interconnection with the soot deposition, which defines the sensor's response.

To burn or not to burn? Impact of in-situ oil burning by-products on marine plankton: A mesocosm experimental approach

<p>In-situ oil burning (isOB) is one of the oil-spill mitigation measures and has been used after some major oil-spill events such as the Deepwater Horizon oil spill in the Gulf of Mexico. Although the ecological impact of oil spills and mitigation measures on the marine ecosystem are of great interest, the toxicity and biodegradation potential of isOB by-products have been poorly addressed and mainly are an unknown.</p><p>We investigated the effects of burned oil residue and soot deposition on the marine plankton communities of the oligotrophic Eastern Mediterranean Sea using a mesocosm experimental approach. Coastal water (collected at 300 m from the coast, north of Crete, Greece) was incubated in 3.5 m<sup>3</sup> mesocosms for 26 days. Three different treatments in triplicates were tested. In one treatment, 2 L of Iranian Crude Oil were added and burned (Burned treatment) while soot was collected and deposited in the form of artificial rain in more mesocosms (Soot treatment) using a custom-designed soot collection apparatus. The third treatment served as the non-contaminated control (Control treatment). Samples were collected at 9 time points (from Day 0 to Day 26) and the plankton, from viruses to micro-plankton, was studied using flow cytometry and inverted microscopy.  </p><p>Although the abundance of prokaryotes was slightly decreased in Burned and Soot treatments compared to the Control, the percentage of active heterotrophic bacteria and their relative size (based on their cytometric characteristics) was higher, which is an indication of increased bacterial activity in the contaminated treatments. Viral to Prokaryote Ratio and pico/nano-eukaryotic abundance were significantly increased in the Burned treatment compared to the Control, which could explain the lower bacterial abundance, despite the estimated increased activity, in the Burned treatment. Also, ciliate abundance was significantly lower in the Burned treatment while the opposite was observed in the Soot treatment (up to three orders of magnitude difference between Burned and Soot) compared to Control. Moreover, soot deposits seem to have had a positive effect on the abundance of dinoflagellates and diatoms.</p><p>To our knowledge, this is the first experiment to study the effects of isOB on whole marine plankton communities. It is evident that the in-situ oil burning has a significant effect on the plankton communities not only at the event site but also on distant areas through the soot deposition.     </p>

Exposure to Heavy Metals in Soot Samples and Cancer Risk Assessment in Port Harcourt, Nigeria

Background. Port Harcourt is an oil-rich city in Nigeria's Niger delta region. For over two years, Port Harcourt experienced black soot deposition in the environment. In November 2016, residents woke up to black soot covering cars, clothes, houses, plants, etc. Soot concentrations continued to increase until the first quarter of 2017. After public outcry, the frequency and concentration of soot deposition began to decline. Objective. The present study was carried out to determine the presence and levels of heavy metals in soot along with a cancer risk assessment of heavy metals exposure in Port Harcourt, Nigeria. Method. Three residential locations were sampled: Aba road, Woji and Iwofe. Sampling was performed from 6:00 am to 6:00 pm, to simulate the estimated duration that most residents who do not work in offices are exposed to soot in places such as the open market and business areas. Five heavy metals (iron (Fe), nickel (Ni), chromium (Cr), cadmium (Cd) and lead (Pb)) were investigated. The data obtained were subjected to Pearson correlation and one-way analysis of variance using SPSS software to test the correlation and significant differences between metals concentrations. Results. Lead was found to have a significant correlation with Cd (0.808), indicating that both metals originated from the same source. Concentrations of heavy metals were higher than control values and the World Health Organization's specifications for ambient air. Chromium concentrations were the lowest. The order of concentration of heavy metals was Fe > Pb > Cd > Ni > Cr. Conclusions. Non-carcinogenic and carcinogenic health risks of these heavy metals were evaluated using the target hazard quotient (THQ) and the incremental lifetime cancer risk (ILCR). Obtained ILCR values were within the acceptable limits for cancer risks. However, the total ILCR values for Cd and Pb for children were 3 times higher than those for adults. This is a source of concern as their prevalence in ambient air puts children and residents in Port Harcourt metropolis at risk of various types of cancers. Competing Interests. The authors declare no competing financial interests.