Microbial responses to mustard gas dumped in the Baltic Sea

Metagenomic Analysis of the Gastrointestinal Microbiota of Gadus morhua callarias L. Originating from a Chemical Munition Dump Site

Several hundred thousand tonnes of munitions containing chemical warfare agents (CWAs) are lying on the seafloor worldwide. CWAs have started leaking from corroded munitions, and their presence in the environment and in organisms inhabiting dump sites has been detected. The presence of CWAs in the water negatively affects fish, macrobenthos and free-living bacteria. It can be expected that the presence of CWAs would also affect the gut-associated bacteria in fish, which are vital for their condition. The main aim of this study was to test if the microbiota of cod collected in the Baltic Bornholm Deep (highly polluted with CWAs) is dysregulated. To investigate this, we conducted metagenomic studies based on 16S rRNA gene sequencing. We found that the microbiota of cod inhabiting the dump site was significantly less taxonomically diverse compared to those from a non-polluted reference site. Moreover, taxa associated with fish diseases (e.g., Vibrionaceae, Aeromonadaceae) were more prevalent, and probiotic taxa (e.g., Actinobacteriota, Rhodobacteraceae) were less frequent in the guts of individuals from the dump site, than those from the reference site. The differences in vulnerability of various bacterial taxa inhabiting cod gastrointestinal tracts to CWAs were hypothesised to be responsible for the observed microbiota dysregulation.

Presence of mercury and methylmercury in Baltic Sea sediments, collected in ammunition dumpsites

Methylmercury (MeHg) is the most toxic and dangerous form of mercury occurring in the environment. MeHg is highly bioaccumulative in organisms and undergoes biomagnification via the food chain. In the Baltic Sea munition dumpsites, methylmercury can be formed from mercury fulminate contained in primary explosives, as environmental conditions there favour methylation. MeHg in analysed sediments ranged from 19 to 2362 pg g^-1d.w., the concentration of mercury (Hg_TOT) ranged from 4 to 294 ng g^-1 d.w., and the values of MeHg/Hg ratio ranged from 0.1 to 2.0%. The obtained results confirmed that munition dumpsites are a source of mercury. The concentration of MeHg is elevated in a wider area than immediately next to dumped munitions. Presented results suggest that physical processes responsible for sediment and near-bottom water movement are diffusing MeHg signal, making munition dumpsites rather a diffuse source of MeHg than a number of point sources associated with particular munitions.

Acute aquatic toxicity of sulfur mustard and its degradation products to Daphnia magna

Sulphur mustard (HD) was the most widely produced chemical warfare agent (CWA) in the history of chemical warfare (CW). Simultaneously, the loads of HD account as by far the largest fraction of the sea-dumped CW. Nowadays its presence in the marine ecosystems recognized as a serious threat for marine users and maritime industries. Although, during over a decade of research much has been done to assess the environmental threats linked with underwater chemical munitions. There are, however, essential gaps in scientific knowledge including scarce information about the aquatic toxicity thresholds of HD and its degradation products. Standardized biotests were performed according to the Organisation for Economic Co-operation and Development (OECD) Test No. 202: Daphnia sp. Acute Immobilisation Test guidelines. Obtained results provide a solid foundation for comparison and categorisation of threats of HD and its degradation products. With the D. magna LC₅₀ aquatic acute toxicity threshold at as low as 224 ± 12 μg × L^-1, 1,2,5-trithiepane is very toxic, being one of the most toxic CWA degradation products that have been investigated up to date. It exhibits stronger effects than 1,4,5-oxadithiepane and diluted HD that turn out to be toxic. In total, the toxicity of 7 compounds has been estimated. Whenever possible, toxicity thresholds were compared with previously existing data originating from different biotests and mathematical modelling.

Bacterial benthic community composition in the Baltic Sea in selected chemical and conventional weapons dump sites affected by munition corrosion

Microflora of marine waters and sediments play a significant role not only in the course of natural changes and circulation of elements in this environment, but can also be a decisive factor during erosion processes of various submerged objects or structures such as wrecks, sunken objects, pipelines, etc. The bacteria which have a significant influence on corrosion processes include aerobic and anaerobic sulfur bacteria as well as iron bacteria. Particular importance is attributed to sulfide reducing bacteria (SRB) which occur in waters, bottom sediments, creating biofilms on metal surface, and may start a process known as microbial induced corrosion (MIC). The occurrence of these bacteria and their populations indicates potential and intensification of corrosion processes. The aim of the study was to determine the number of microorganisms from various groups in the Baltic Sea sediments, especially those that are active in biological corrosion processes. This data can be used for a study comprehensive of corrosive processes in the marine environment, and as a result, to carry out a real assessment of the risks arising from the release of toxic substances into the environment from conventional and chemical weapons lying on the bottom caused by progressing corrosive processes, including biological corrosion. The article presents the results of research on the presence and accounts of microorganisms in bottom sediment samples taken from the dump sites of chemical and conventional ammunition in the Baltic Sea. Particular attention was paid to halophilic and halotolerant bacteria due to their significant contribution to both corrosion and decomposition processes of CWA and explosives, particularly in the saltwater environment. There were high and quite similar numbers of mesophilic, psychrophilic and halophilic bacteria in the studied samples, while significantly smaller numbers of anaerobic bacteria. The amount of mesophilic bacteria ranges from 6.42*10³ to 2.85*10⁷, on average 4.5*10⁶ in 1 g DM, psychrophilic from 5.73*10³ in1g DM to 4.11*10⁷ in 1 g DM, on average 6.44*10⁶ in 1 g DM, whereas for halophylic from 4.09*10² to 5.60*10⁷, on average 5.83*10⁶ in1g DM. The numbers of fungi were at a much lower level and ranged from 4.65*10¹ to 8.08*10², on average 2.63*10² in 1 g DM. mesophilic fungi and from 0 to 1.60*10³, on average 3.58*10² in 1 g DM for psychrophilic fungi. The presence of sulfide reducing bacteria (SRB) was also detected in large populations, especially when they were isolated by means of the medium prepared with seawater (from 9.72 to 5.36*10², on average 2.52*10² in 1 g DM), which indicates their adaptation to the saline environment and promotes of biological anaerobic processes, including corrosive processes. No significant amounts of iron bacteria were found, probably due to the small amount of oxygen in the sampling area. The small number of iron bacteria indicates that primarily anaerobic sulfide reducing bacteria (SRB) have the major part in the microbial corrosion phenomena.

Baltic Sea methanogens compete with acetogens for electrons from metallic iron

Microbially induced corrosion of metallic iron (Fe⁰)-containing structures is an environmental and economic hazard. Methanogens are abundant in low-sulfide environments and yet their specific role in Fe⁰ corrosion is poorly understood. In this study, Sporomusa and Methanosarcina dominated enrichments from Baltic Sea methanogenic sediments that were established with Fe⁰ as the sole electron donor and CO₂ as the electron acceptor. The Baltic-Sporomusa was phylogenetically affiliated to the electroactive acetogen S. silvacetica. Baltic-Sporomusa adjusted rapidly to growth on H₂. On Fe⁰, spent filtrate enhanced growth of this acetogen suggesting that it was using endogenous enzymes to retrieve electrons and produce acetate. Previous studies have proposed that acetate produced by acetogens can feed commensal acetoclastic methanogens such as Methanosarcina. However, Baltic-methanogens could not generate methane from acetate, plus the decrease or absence of acetogens stimulated their growth. The decrease in numbers of Sporomusa was concurrent with an upsurge in Methanosarcina and increased methane production, suggesting that methanogens compete with acetogens for electrons from Fe⁰. Furthermore, Baltic-methanogens were unable to use H₂ (1.5 atm) for methanogenesis and were inhibited by spent filtrate additions, indicating that enzymatically produced H₂ is not a favorable electron donor. We hypothesize that Baltic-methanogens retrieve electrons from Fe⁰ via a yet enigmatic direct electron uptake mechanism.

Deep sea habitats in the chemical warfare dumping areas of the Baltic Sea

The Baltic Sea is a severely disturbed marine ecosystem that has previously been used as a dumping ground for Chemical Warfare Agents (CW). The presence of unexploded underwater ordnance is an additional risk factor for offshore activities and an environmental risk for the natural resources of the sea. In this paper, the focus is on descriptions of the marine habitat based on the observations arising from studies linked to the CHEMSEA, MODUM and DAIMON projects. Investigated areas of Bornholm, Gotland and Gdańsk Deeps are similarly affected by the Baltic Sea eutrophication, however, at depths greater than 70m several differences in local hydrological regimes and pore-water heavy metal concentrations between those basins were observed. During the lifespan of presented studies, we were able to observe the effects of Major Baltic Inflow, that started in December 2014, on local biota and their habitats, especially in the Bornholm Deep area. Reappearance of several meiofauna taxa and one macrofauna specimen was observed approximately one year after this phenomenon, however it's ecological effects already disappeared in March 2017. According to our findings and to the EUNIS Habitat Classification, the three reviewed areas should be characterized as Deep Sea Muddy Sands, while the presence of suspicious bomb-like objects both beneath and on top of the sediments confirms their CW dumpsite status.

The problem of dephosphorization using waste recycling

The article considers optimizing methods for wastewater treatment systems. Nutrients (nitrogen and phosphorus) are discharged from the river basin of the northwest Russia. Disruption of ecological safety and healthy state of water basins takes place when excess amount of nitrogen and phosphorus is discharged from wastewater. This results in eutrophication that is increased growth of seaweeds and, therefore, in ecological system disruption. The cities of the northwest region are short of funds for renovation of water treatment systems. However, the new solution lies in improvement of biological water treatment system by means of chemical injection. The main research task is implementation of methods for enhanced biological phosphorus removal from domestic sewage. The problem of recycling and ecological safety of rivers within the northwest of Russia and the Baltic Sea is not solved completely. That is why for wastewater dephosphorization, the authors suggest using sulfuric acid production waste at chemical plant "Ammophos," Cherepovets (ferrous sulfate FeSO₄·7H₂O and phosphogypsum СаSO₄·Р₂О₅), as reagents. The advantage of these reagents is their low cost. The authors show the efficiency of the new optimal reagent's combination. Filtering the wastewater through sand filters after secondary settlers increases the total phosphorus removal efficiency up to 90%. The high effect of all types of phosphorus and total nitrogen removal from wastewater can be resulted from the features of micelle creation during coagulation.

Sea-dumped chemical weapons: environmental risk, occupational hazard

INTRODUCTION

Chemical weapons dumped into the ocean for disposal in the twentieth century pose a continuing environmental and human health risk.

OBJECTIVE

In this review we discuss locations, quantity, and types of sea-dumped chemical weapons, related environmental concerns, and human encounters with sea-dumped chemical weapons.

METHODS

We utilized the Ovid (http://ovidsp.tx.ovid.com) and PubMed (http://www.pubmed.org) search engines to perform MEDLINE searches for the terms 'sea-dumped chemical weapons', 'chemical warfare agents', and 'chemical munitions'. The searches returned 5863 articles. Irrelevant and non-English articles were excluded. A review of the references for these articles yielded additional relevant sources, with a total of 64 peer-reviewed articles cited in this paper. History and geography of chemical weapons dumping at sea: Hundreds of thousands of tons of chemical munitions were disposed off at sea following World War II. European, Russian, Japanese, and United States coasts are the areas most affected worldwide. Several areas in the Baltic and North Seas suffered concentrated large levels of dumping, and these appear to be the world's most studied chemical warfare agent marine dumping areas. Chemical warfare agents: Sulfur mustard, Lewisite, and the nerve agents appear to be the chemical warfare agents most frequently disposed off at sea. Multiple other type of agents including organoarsenicals, blood agents, choking agents, and lacrimators were dumped at sea, although in lesser volumes. Environmental concerns: Numerous geohydrologic variables contribute to the rate of release of chemical agents from their original casings, leading to difficult and inexact modeling of risk of release into seawater. Sulfur mustard and the organoarsenicals are the most environmentally persistent dumped chemical agents. Sulfur mustard in particular has a propensity to form a solid or semi-solid lump with a polymer coating of breakdown products, and can persist in this state on the ocean floor for decades. Rates of solubility and hydrolysis and levels of innate toxicity of a chemical agent are used to predict the risk to the marine environments. The organoarsenicals eventually breakdown into arsenic, and thus present an indefinite timeline for contamination. Generally, studies assaying sediment and water levels of parent chemical agents and breakdown products at dumpsites have found minimal amounts of relevant chemicals, although arsenic levels are typically higher in dumpsites than reference areas. Studies of marine organisms have not shown concerning amounts of chemical agents or breakdown products in tissue, but have shown evidence of chronic toxicity. There is believed to be minimal risk posed by seafood consumption. Microbiota assays of dumpsites are significantly altered in species composition compared to reference sites, which may imply unseen but significant changes to ecosystems of dumpsites. Human health concerns: The major human health risk at this time appears to arise from acute exposure to an agent by either accidental recovery of a chemical weapon on a fishing vessel, or by munitions washed ashore onto beaches.

CONCLUSIONS

Improving technology continues to make the deep sea more accessible, thus increasing the risk of disturbing munitions lying on or buried in the seabed. Pipe laying, cable burying, drilling, scuba diving, trawling, and undersea scientific research are the activities posing the most risk. The long-term threat to the benthic habitat via increased arsenic concentrations, shifts in microbiota speciation, and chronic toxicity to vertebrates and invertebrates is not currently understood. The risk to the environment of massive release via disturbance remains a distinct possibility. Terrorist recovery and re-weaponization of chemical agents is a remote possibility.

Spatially differing bacterial communities in water columns of the northern Baltic Sea

The Baltic Sea is a large, shallow, and strongly stratified brackish water basin. It suffers from eutrophication, toxic cyanobacterial blooms, and oxygen depletion, all of which pose a threat to local marine communities. In this study, the diversity and community structure of the northern Baltic Sea bacterial communities in the water column were, for the first time, thoroughly studied by 454 sequencing. The spring and autumn bacterial communities were one order of magnitude less diverse than those in recently studied oceanic habitats. Patchiness and strong stratification were clearly detectable; <1% of operational taxonomic units were shared among 11 samples. The community composition was more uniform horizontally (at a fixed depth) between different sites than vertically within one sampling site, implying that the community structure was affected by prevailing physical and hydrochemical conditions. Taxonomic affiliations revealed a total of 23 bacterial classes and 169 genera, while 5% of the sequences remained unclassified. The cyanobacteria accounted for <2% of the sequences, and potentially toxic cyanobacterial genera were essentially absent during the sampling seasons.

Environmental hazards of sea-dumped chemical weapons

Does the post-WWII burial at sea of chemical weapons still pose a human and environmental risk?