Background, aim and scope The paper presents concentrations of trace elements in blood of homebred animals (cows and sheep) from Southern Serbia (Bujanovac) and the contents of natural and anthropogenic radionuclides and some heavy metals in feed. The region of Southern Serbia was exposed to contamination by depleted uranium ammunition during NATO attacks in 1999 and therefore, is of great concern to environmental pollution and human and animal health. Materials and methods Conventional instrumental and epithermal neutron activation analyses are used to measure trace elements in cow and sheep blood samples collected randomly at six locations in the region of Bujanovac (village of Borovac) in the spring of 2005. Samples of feed (grass and crops: corn, wheat and oats), collected on the same locations (households), are analysed for the contents of radionuclides on an HPGe detector (Ortec, relative efficiency 23%) by standard gamma spectrometry. The content of Hg, Pb and Cd in feed is determined by standard atomic absorption spectrometry on the VarianSpectra220/ThermoSolar GFS97 spectrometer. Results Concentrations of 29 elements (Na, Al (P), Cl, K, Sc, Cr, Mn, Ni, Fe, Co, Zn, Se, As, Br, Sr, Rb, Sb, In, I, Ba, Cs, La, Nd, Eu, Sm, Tb, Hf, Ta and Th) are determined in blood of the examined animals. In feeds, natural ⁴⁰K is found in all of the samples, cosmogenic ⁷Be and fission product ¹³⁷Cs are detected only in the grass samples, while heavy metals Hg, Cd and Pb are found in the range of 0.01-0.02, 0.84-1.15 and 0.74-7.34 mg/kg, respectively. Calculated soil-to-blood transfer factors are in a wide range of 8·10⁻⁶ to 64, as a result of varying significance of the elements in animal metabolism and feeding habits. Discussion The results of trace elements' concentrations in animal blood are in good agreement with available data for K, Ni, Zn, Se and Rb. Higher Br concentrations in animal blood are most probably caused by large biomass burning events during blood sampling. Very low concentration of Fe in cows and sheep confirms the results of previous biochemical studies on animal anaemia in the region. High concentration of As correlates with geochemical peculiarities of the Balkans and is also likely influenced by the use of pesticides in the agricultural production. For some of the elements (La, Nd, Eu, Sm, Tb, Sb, Hf, Ta, Th, In, Ba, Sr, Sc and Cs), there are few or no literature data. Therefore, some of the presented data are significant not only for the country and the region, but on a wider scale. Activities of natural radionuclides in feeds are within the average values reported for the region, while the activities of ²¹⁰Pb and ²³⁵/²³⁸U are below the limit of detection. This is in accordance with previous investigations showing no widespread contamination by depleted uranium in the area. Contents of Hg and Pb in feeds are below the nationally permissible levels, unlike the content of Cd which exceeds it, probably caused by the use of phosphate fertilisers and fossil fuel combustion in the area. Conclusions In general, the concentrations of trace elements in blood of homebred cows and sheep are in good agreement with reference materials, available literature data and the results of previous studies in the area. The exceptions are Fe, As and Br. The contents of natural and anthropogenic radionuclides in feeds are within the expected levels, and there are no signs of contamination by depleted uranium or other fission products. Apart from Cd, there are no signs of pollution by heavy metals in feeds. The highly sensitive method of instrumental neutron activation analysis provides data on the concentration of some elements in animal blood not previously reported for the region and elsewhere. Recommendations and perspectives The presented study is a part of the long term ongoing project on the health risk assessment on animals and humans in the region. The collected data is intended to provide a base for the animal and human risk assessment as well as an estimate of the general pollution status of the environment in the region. Since some of the investigated elements are classified as important trace elements for livestock, the results could also be used to balance and improve the animal diet and thus, improve the growth and reproduction rate.

Purpose As one component of the German ecological environment observation, the Environmental Specimen Bank program was initiated in the mid-1980s. Under the program, representative specimens of marine, fresh water, and terrestrial ecosystems are sampled regularly and archived under chemically stable conditions. An initial characterization of the samples provides data regarding the status quo of the respective ecosystems. The aim of the present publication is to give insight into these real-time monitoring data, which have been generated for the last 10 to 20 years. This is done exemplarily for the heavy metals cadmium (Cd), mercury (Hg), and lead (Pb) in marine specimens of the Baltic and the North Sea. Methods Bladder wrack (Fucus vesiculosus), blue mussel (Mytilus edulis), eelpout (Zoarces viviparus), and eggs of herring gulls (Larus argentatus) were sampled at one location in the Baltic Sea and at two sites in the North Sea (Schleswig-Holstein Wadden Sea and Lower Saxony Wadden Sea). Annual samples were pooled, homogenized, and analyzed for a set of elements. Cd and Pb were quantified after freeze-drying and microwave digestion using inductively coupled plasma-mass spectrometry. Total Hg in freeze-dried samples was determined by atomic absorption spectrometry using a direct mercury analyzer. Results Time series data covering up to two decades revealed comparable cadmium levels at all three locations. Concentrations in bladder wrack ranged between 0.10 and 0.37 µg/g on a wet weight basis (ww). Respective values for blue mussel and eelpout liver were 0.07-0.29 and 0.01-0.10 µg/g ww. Herring gull eggs were not included in cadmium analyses. Declining trends were observed in North Sea bladder wrack and mussels, eelpout from the Lower Saxony site, and mussels from the Baltic Sea. Upward trends were apparent in eelpout from the Schleswig-Holstein location. Mercury concentrations in Baltic Sea specimens ranged from 1.1-2.7 ng/g ww in bladder wrack to 2.6-5.1, 26-52, and 86-226 ng/g ww in blue mussel, eelpout muscle, and herring gull eggs, respectively. No temporal trends were observed. North Sea bladder wrack had accumulated 5.4-24 ng/g ww Hg. The respective Hg values for blue mussel and eelpout muscle were 19-64 and 73-187 ng/g ww. Highest Hg contents were detected in herring gull eggs (90-1,100 ng/g ww). Declining trends of Hg were observed in herring gull eggs at both North Sea locations and in blue mussels at the Lower Saxony site. Lead concentrations in Baltic Sea specimens were 48-222 ng/g ww in bladder wrack, 85-189 ng/g ww in blue mussel, 2.0-9.5 and 10-42 ng/g ww in eelpout muscle and liver, and 2.7-26 ng/g ww in herring gull eggs. In the North Sea, Pb concentrations were as follows: 68-397 ng/g ww in bladder wrack, 101-507 ng/g ww in blue mussels, 2.6-35 and 5.9-158 ng/g ww in eelpout muscle and liver, and 3.5-55 ng/g ww in herring gull eggs. Highest Pb-levels were found at the Lower Saxony site. Declining Pb-trends were observed in bladder wrack from the Baltic Sea; in bladder wrack and mussel at the Schleswig-Holstein location; and in bladder wrack, mussels, eelpout liver, and herring gull eggs at the Lower Saxony site. Conclusions During the 10 to 20 years of monitoring, reliable data were obtained which allow a good insight into metal contamination of marine biota. Assessment of the data according to OSPAR criteria (OSPAR 2005) revealed cadmium levels above the derived background concentrations in mussels of all three sites. Mercury levels above background concentrations were found at both North Sea locations, whereas only mussels at the Lower Saxony site had Pb concentrations above the reference value. Archived specimens are available for further analyses and questions which may arise in the future (speciation of elements, metallomics).

Background and purpose In Pakistan, almost 70% of the population lives in rural areas. Ninety-four percent of households in rural areas and 58% in urban areas depend on biomass fuels (wood, dung, and agricultural waste). These solid fuels have poor combustion efficiency. Due to incomplete combustion of the biomass fuels, the resulting smoke contains a range of health-deteriorating substances that, at varying concentrations, can pose a serious threat to human health. Indoor air pollution accounts for 28,000 deaths a year and 40 million cases of acute respiratory illness. It places a significant economic burden on Pakistan with an annual cost of 1% of GDP. Despite the mounting evidence of an association between indoor air pollution and ill health, policy makers have paid little attention to it. This review analyzes the existing information on levels of indoor air pollution in Pakistan and suggests suitable intervention methods. Methods This review is focused on studies of indoor air pollution, due to biomass fuels, in Pakistan published in both scientific journals and by the Government and international organizations. In addition, the importance of environmental tobacco smoke as an indoor pollutant is highlighted. Results Unlike many other developing countries, there are no long-term studies on the levels of indoor air pollution. The limited studies that have been undertaken indicate that indoor air pollution should be a public health concern. High levels of particulate matter and carbon monoxide have been reported, and generally, women and children are subject to the maximum exposure. There have been a few interventions, with improved stoves, in some areas since 1990. However, the effectiveness of these interventions has not been fully evaluated. Conclusion Indoor air pollution has a significant impact on the health of the population in Pakistan. The use of biomass fuel as an energy source is the biggest contributor to poor indoor air quality followed by smoking. In order to arrest the increasing levels of indoor pollution, there is a dire need to recognize it as a major health hazard and formulate a national policy to combat it. An integrated effort, with involvement of all stakeholders, could yield promising results. A countrywide public awareness campaign, on the association of indoor air pollution with ill health, followed by practical intervention would be an appropriate approach. Due to the current socioeconomic conditions in the country, development and adoption of improved cooking stoves for the population at large would be the most suitable choice. However, the potential of biogas as a fuel should be explored further, and modern fuels (natural gas and LPG) need to be accessible and economical. Smoking in closed public spaces should be banned, and knowledge of the effect of smoking on indoor air quality needs to be quantified.

Background, aim, and scope Chlorinated volatile organic compounds (CVOCs), widely used in industry as solvents and chemical intermediates in the production of synthetic resins, plastics, and pharmaceuticals, are highly toxic to the environment and public health. Various studies reported that Fenton's oxidation could degrade a variety of chlorinated VOCs in aqueous solutions. In acidic conditions, ferrous ion catalyzes the decomposition of H₂O₂ to form a powerful •OH radical. In this study, wastewater from wash of ion-exchange resin containing typical CVOC, 1,2-dichloroethane, was treated using Fenton's oxidation. To reduce environmental load and processing costs of wastewater, Fenton process as a simple and efficient treatment method was applied to degrade 1,2-dichloroethane of wash water. Materials and methods The water samples were collected from three different washing stages of ion-exchange resin. The degradation of 1,2-dichloroethane and total organic carbon (TOC) of wash water of ion-exchange resin by Fenton process was studied with response surface method (RSM). Design of the experiments was conducted by central composite face, and factors included in three models were Fe²⁺ and H₂O₂ doses and treatment time. Relevant quadratic and interaction terms of factors were investigated. Results According to ANOVA, the model predicts well 1,2-dichloroethane reduction of all water samples and TOC reduction of samples 2 and 3. The Fe²⁺ and H₂O₂ doses used in the present study were most suitable when 1,2-dichloroethane concentration of the wash water is about 120 mg L⁻¹. In that case, Fenton's oxidation reduced 1,2-dichloroethane and TOC up to 100% and 87%, respectively, according to the RSM model. With 90-min reaction time and H₂O₂ dose of 1,200 mg L⁻¹, the required Fe²⁺ doses for 1,2-dichloroethane and TOC were 300 and 900 mg L⁻¹, respectively. The optimal H₂O₂/Fe²⁺ stoichiometric molar ratio was between 4-6. Then, concentration of Fe²⁺ was low enough and the amount of residual sludge can thus be reduced. It seems that most of TOC and part of 1,2-dichloroethane were removed by coagulation. Discussion Up to a certain extent, increase of Fe²⁺ and H₂O₂ doses improved the removal of 1,2-dichloroethane and TOC. High Fe²⁺ doses increased the formation of ferric-based sludge, and excessive H₂O₂ doses in sample 2 decreased the degradation of 1,2-dichloroethane. Excess amount of hydrogen peroxide may scavenge hydroxyl radicals, thus leading to loss of oxidative power. Also, the residual hydrogen peroxide of different samples increased with increasing H₂O₂ dose and H₂O₂/Fe²⁺ molar ratio and decreasing treatment time probably also due to scavenging reactions. Due to the saturated nature of 1,2-dichloroethane, the oxidation mechanism involves hydrogen abstraction before addition of hydroxyl radical, thus leading to lower rate constants than for direct hydroxyl radical attack, which for one increases the treatment time. Conclusions Complete removal of 1,2-dichloroethane was attained with initial concentration <120 mg L⁻¹. Also, TOC degraded effectively. Wash water with higher concentration of 1,2-dichloroethane requires longer treatment times and higher concentrations of Fe²⁺ and H₂O₂ for sufficient 1,2-dichloroethane removal. Recommendations and perspectives Due to the results achieved in this study, Fenton's oxidation could be recommended to be used for organic destruction of wash water of ion-exchange resin. Residual sludge, the main disadvantage in Fenton process, can be reduced by optimizing the ferrous dose or by using heterogeneous treatment where most of the reusable iron remains in the solid phase.

Background, aim, and scope The occurrence and fate of pharmaceuticals in the aquatic environment is recognized as one of the emerging issues in environmental chemistry and as a matter of public concern. Existing data tend to focus on the concentrations of pharmaceuticals in the aqueous phase, with limited studies on their concentrations in particulate phase such as sediments. Furthermore, current water quality monitoring does not differentiate between soluble and colloidal phases in water samples, hindering our understanding of the bioavailability and bioaccumulation of pharmaceuticals in aquatic organisms. In this study, an investigation was conducted into the concentrations and phase association (soluble, colloidal, suspended particulate matter or SPM) of selected pharmaceuticals (propranolol, sulfamethoxazole, meberverine, thioridazine, carbamazepine, tamoxifen, indomethacine, diclofenac, and meclofenamic acid) in river water, effluents from sewage treatment works (STW), and groundwater in the UK. Materials and methods The occurrence and phase association of selected pharmaceuticals propranolol, sulfamethoxazole, meberverine, thioridazine, carbamazepine, tamoxifen, indomethacine, diclofenac, and meclofenamic acid in contrasting aquatic environments (river, sewage effluent, and groundwater) were studied. Colloids were isolated by cross-flow ultrafiltration (CFUF). Water samples were extracted by solid-phase extraction (SPE), while SPM was extracted by microwave. All sample extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the multiple reaction monitoring. Results and discussion Five compounds propranolol, sulfamethoxazole, carbamazepine, indomethacine, and diclofenac were detected in all samples, with carbamazepine showing the highest concentrations in all phases. The highest concentrations of these compounds were detected in STW effluents, confirming STW as a key source of these compounds in the aquatic environments. The calculation of partition coefficients of pharmaceuticals between SPM and filtrate (observed partition coefficients, [graphic removed] , [graphic removed] ), between SPM and soluble phase (intrinsic partition coefficients, [graphic removed] , [graphic removed] ), and between colloids and soluble phase (K coc) showed that intrinsic partition coefficients [graphic removed] are between 25% and 96%, and between 18% and 82% higher than relevant observed partition coefficients values, and are much less variable. Secondly, K coc values are 3-4 orders of magnitude greater than [graphic removed] values, indicating that aquatic colloids are substantially more powerful sorbents for accumulating pharmaceuticals than sediments. Furthermore, mass balance calculations of pharmaceutical concentrations demonstrate that between 23% and 70% of propranolol, 17-62% of sulfamethoxazole, 7-58% of carbamazepine, 19-84% of indomethacine, and 9-74% of diclofenac are present in the colloidal phase. Conclusions The results provide direct evidence that sorption to colloids provides an important sink for the pharmaceuticals in the aquatic environment. Such strong pharmaceutical/colloid interactions may provide a long-term storage of pharmaceuticals, hence, increasing their persistence while reducing their bioavailability in the environment. Recommendations and perspectives Pharmaceutical compounds have been detected not only in the aqueous phase but also in suspended particles; it is important, therefore, to have a holistic approach in future environmental fate investigation of pharmaceuticals. For example, more research is needed to assess the storage and long-term record of pharmaceutical residues in aquatic sediments by which benthic organisms will be most affected. Aquatic colloids have been shown to account for the accumulation of major fractions of total pharmaceutical concentrations in the aquatic environment, demonstrating unequivocally the importance of aquatic colloids as a sink for such residues in the aquatic systems. As aquatic colloids are abundant, ubiquitous, and highly powerful sorbents, they are expected to influence the bioavailability and bioaccumulation of such chemicals by aquatic organisms. It is therefore critical for colloids to be incorporated into water quality models for prediction and risk assessment purposes.

Background, aim and scope Polychlorinated biphenyls (PCB) and dichlorodiphenyltrichloroethane (DDT) concentrations were determined in the liver of two deep sea fish species, Mediterranean slimehead and blackfin sorcerer, from the Adriatic Sea (southeastern Mediterranean Sea). Results and discussion The examination of congener profiles showed that hexachlorinated molecules were dominant (hexa-CBs, 55.3-56.2%), followed by penta-CBs (21.5-21.8%) and hepta-PCB 180 (14.9-16.0%). PCB 138, 153 and 180 were the prominent congeners accounting for 69.3% of the total PCBs. Among the compounds of DDT, p,p′-DDE was the most dominant molecule (Mediterranean slimehead, 86.6%; blackfin sorcerer, 92.8%), demonstrating the old age of these compounds in the environment. In both species, PCB contents were higher than those of DDTs. Contaminant load was higher in Mediterranean slimehead (PCBs, 1,086 ng g⁻¹ lipid weight; DDTs, 799 ng g⁻¹ lipid weight) than in blackfin sorcerer (PCBs, 561 ng g⁻¹ lipid weight; DDTs, 224 ng g⁻¹ lipid weight). Conclusion The high ratios ΣPCBs/ΣDDTs indicated predominantly industrial versus agrarian activities in the area. Dioxins toxic equivalent (TEQ) concentrations (8.1-18.7 pg TEQ per gram wet weight) reached those encountered in marine organisms at higher levels in the trophic chain, revealing the onerous status of contamination by PCBs in Mediterranean deep sea biota.

Background, aim and scope Ria de Aveiro (Portugal) is a shallow coastal lagoon of high economic and ecological importance. Hardly any data on its chemical pollution by polar organic pollutants are available in literature. This study focused on the presence and sources of a series of phenolic endocrine-disrupting compounds (EDCs) in this area, including parabens, alkylphenolic compounds and bisphenol-A (BPA). A number of possible sources of pollution are present in the area, including the large harbours present in the lagoon, the city of Aveiro and the rivers discharging into the area. A recently constructed submarine wastewater outfall, located a few kilometres from the lagoon inlet has also been suggested as a possible source of pollution to Ria de Aveiro in several publications. The aim of the current field study was to investigate the occurrence and main sources of phenolic endocrine disruptors in Ria de Aveiro. Materials and methods An extensive sampling campaign was performed, with surface water and wastewater grab samples taken at over 50 locations, in duplicate on different days. Samples were treated using solid phase extraction and analysed by liquid chromatography tandem mass spectrometry. Results and discussion Concentrations in lagoon water were generally low: not exceeding 20 ng/L for most analytes. Levels in river water exceeded those in the lagoon by a factor 3 to 500 (o-phenylphenol (PhP) and nonylphenoxy ethoxy acetic acids (A₉PEC), respectively), with concentrations up to 700 ng/L for BPA and 7,300 ng/L for A₉PEC. Samples from the harbours showed EDC levels similar to those in the rest of the lagoon, but in the city of Aveiro, elevated concentrations were observed for alkylphenol ethoxylates (A₉PEO), A₉PEC, PhP and BPA. Wastewater effluents showed low levels for parabens, whilst alkylphenolic compounds reached several micrograms per litre. The effluents are discharged into the ocean via a submarine outfall, but as marine water near the outfall showed slightly elevated concentrations only for A₉PEO, it does not seem to be a significant source of these EDCs for the area. Conclusions All the studied phenolic EDCs were detected in the study area, with high levels found in some of the rivers discharging into the lagoon, and generally low concentrations in the lagoon itself. The main sources for all investigated EDCs were the rivers Caster and Antuã which discharge into the lagoon. The city of Aveiro was identified as a secondary source. As the tidal water exchange volume is much larger than the freshwater input from the rivers, concentrations of phenolic EDCs remained low in the lagoon.

Background, aim, and scope In this study, a suite of sublethal stress biomarkers were analyzed in juveniles of the sentinel species, the Pacific oyster Crassostrea gigas, with a view to using them as pollution monitoring tools. The aim of this work was (1) to study baseline seasonal variations of biomarkers in different body compartments of C. gigas in the reference site and, after selecting biomarkers presenting no seasonal variations, (2) to compare responses of these biomarkers between contaminated and reference sites. Materials and methods Juvenile oysters were transplanted from Bouin (France), a reference site, to three different sites in Marennes-Oleron Bay (France), located in another water body and next to different contamination sources. Animals were exposed in situ for 3 months in summer, autumn, and winter. The following biomarkers were measured: superoxide dismutase (SOD) and glutathione peroxidase (GPx) in gills and digestive gland and lysozyme and phenoloxidase (PO) in plasma. Results No significant seasonal variations for SOD in gills and digestive gland, GPx in gills, and PO in plasma were observed in the reference site. Significant differences in enzyme activity were observed between contaminated and reference sites for SOD in gills and digestive gland and PO in plasma, depending on the body compartment, the season, and/or the site. Conclusions In conclusion, these data suggest the potential application of these biomarkers in C. gigas to provide ecologically relevant information and, therefore, to be used as biomarkers in coastal pollution monitoring.

Background, aim, and scope We recently developed a new isolation method for diesel exhaust particles (DEP), involving successive extraction with H₂O, sodium bicarbonate, and sodium hydroxide, in which the sodium hydroxide extract was found to consist of phenolic components. Analysis of the extract revealed that vasodilative-active nitrophenols are in DEP in significantly higher concentrations than those estimated by an earlier method involving a combination of solvent extraction and repeated chromatography. These findings indicated that our new procedure offers a simple, efficient, and reliable method for the isolation and identification of bioactive substances in DEP. This encouraged us to extend our work toward investigating new vasodilatory substances in the sodium bicarbonate extract. Materials and methods DEP were collected from the exhaust of a 4JB1-type engine (ISUZU Automobile Co., Tokyo, Japan). GC-MS analysis was performed with a GCMS-QP2010 instrument (Shimadzu, Kyoto, Japan). Results DEP dissolved in 1-butanol was successively extracted with water, sodium bicarbonate, and then aqueous sodium hydroxide. The sodium bicarbonate extract was neutralized and the resulting mixture of acidic components was subjected to reverse-phase (RP) column chromatography followed by RP-HPLC with fractions assayed for vasodilative activity. This led to the identification of terephthalic acid, p-hydroxybenzoic acid, isophthalic acid, phthalic acid, 3-hydroxy-4-nitrobenzoic acid, 4-hydroxy-3-nitrophenol, and 1,4,5-naphthalene tricarboxylic acid as components of DEP. Discussion The sodium bicarbonate extract was rich in aromatic carboxylic acid components. Repeated reverse-phase chromatography resulted in the successful isolation of several acidic substances including the new vasodilative materials, 4-hydroxy-3-nitrobenzoic acid, and 3-hydroxy-4-nitrobenzoic acid. Conclusions Our new fractionation method for DEP has made possible the isolation of new vasodilative compounds from the sodium bicarbonate extract.

Purpose China's freshwater subtropical shallow lakes are increasingly eutrophic and susceptible to production of heavy growths or water blooms of cyanobacteria. One example was the heavy water bloom that occurred for the first time in Lake Xuanwu, in 2005, an urban lake located in Nanjing city. The aim of the present study was to determine dynamics of water bloom dominating Microcystis in this lake. Meanwhile, the relationship between environmental factors and Microcystis populations was also analyzed. Materials and methods Molecular detection, using quantitative polymerase chain reaction, was used in this lake to study the dynamics of the cyanobacterial community, its Microcystis populations, and the microcystin-producing Microcystis genotypes from August 2005 to November 2006. Results It was shown that Microcystis wesenbergii and Microcystis aeruginosa were the main components of the cyanobacterial blooms in Lake Xuanwu, and they coexisted with species of the filamentous cyanobacterial genera Anabaena, Planktothrix, and Anabaenopsis. Microcystis cells were detected during the entire survey period and in all sample sites. The cell abundance of Microcystis ranged from 3.6 × 10² cells ml⁻¹ to a peak of 3.8 × 10⁶ cells ml⁻¹. The ratio of mcyB-containing Microcystis subpopulations to the total Microcystis varied, ranging from 0.1% to 12.8%. The abundance of Microcystis containing the mcyB microcystin gene was shown to be significantly correlated with concentrations of total phosphorus and phosphate. Conclusions Water temperature was the primary factor affecting Microcystis abundance in the lake, and phosphorus loading was shown to be a main factor in governing the growth of both microcystin-producing genotype and total Microcystis population. Higher Microcystis cell counts at the bottom of the water column before and after appearance of water blooms in Lake Xuanwu suggested that Microcystis numbers in the water column, especially at the bottom of the water column, play an important role in forming the next water bloom.