The wildfire occurring in the past weeks in Pedrógão Grande, eastern Portugal and near Doñana National Park in southern Spain, ended with an enormous lives lost (64 people in Portugal) and the evacuation of more than 10,000 people from the surrounding areas. The fires affected 30,000 hectares in Portugal and almost 10,000 ha in Spain. Hundreds of firefighters and volunteers worked to combat the blaze and the flames that overwhelmed the trees for days. In both sites the fires seems to be the results of “forest management errors and bad political decisions” by governments in the recent decades. In the special case of Doñana, a UNESCO World Heritage Site and a Biosphere Reserve, WWF Spain claimed from several years the hazard of forest fires due to the uncontrolled extent of public forest for different uses (www.). Between 2005 and 2009, WWF Spain signaled the presence of a total of 80 fires in the Doñana area that affect the wildlife in one the most extended coastal wetland from southern Europe.
Forest fires usually occur in nature and play an essential ecological role in maintaining the ecosystem health, contributing to forests regeneration, stimulation of seed germination and the returning of important nutrients to the forest soil previously stored in biomass. After a natural forest fire, starts a process of ecological succession where the ecosystems pass it to several changes and develop in a mature forest again. This means a recolonization of the soil with herbaceous species, grasses and weeds, followed by taller plants and the last comers are tree species. Natural wildfires also influence the hydrological cycle immediately after post-fire period as well as the water quality at the surface and underground.
The most evident changes in surface waters post-fire are sediments loads particularly in suspended fraction in streams that affect temporary the biological habitats available for aquatic organisms from the streams channel and the riparian zone, such are fishes and benthic and interstitial invertebrates. The changes in water chemical properties after a wildfire are not well documented, but the studies suggest an increase of nutrients loads, and especially of phosphorus and nitrogen. An estimation of the nitrogen content in a wildfire from a forest experimental area in California suggest that the nitrogen might be 10 times higher post-fires events and its concentration remains higher even after three years (Westerling & Bryant, 2008). However, the increment of nutrient loads after a fire event highly depends by the watershed, type of forest and local/regional climatic conditions. Groundwater in forested areas is usually pristine, since the soil forest significantly contributes to water purification. The primary source of groundwater contamination after a fire, results from microorganisms that can enter underground due to the soil destruction, sediments loads, ash and potential changes in water pH. Post-fire there is a high alkalinity runoff from burned areas that may increase temporary the pH in both surface and groundwater, but this can be neutralized if it is diluted in sufficient quantities of water.
On medium and long term wildfires are beneficial for the ecosystems, either terrestrial (vegetation) or aquatic (surface and groundwater). However, an important aspect resulted from the wildfires is the contamination with fire extinguishing agents. These chemical substances called flame retardants are used worldwide since the beginning of the 1970. Flame retardants are chemical compounds that suppress the flames and are used as a prevention measures or when a fire is already occurring. Airplanes also release flame retardants into the forests, and they are usually applied as prevention in well-known areas susceptible to fires, or when the fire is already occurring. They are able to alter the combustion even after the water is removed by evaporation during burning.
Flame retardants consist in a mixture of water (85%), inorganic chemicals (10%) and coloring agents and stabilizers (5%). The most common inorganic chemicals used nowadays are based on ammonia (phosphates and sulphates of ammonia) or brome. In the past, all retardants contained sodium ferrocyanide as a corrosion inhibitor, but due to their toxicity especially UV irradiation they were banned since 2007. Flame retardants are also present around us in plastics, textiles, electronic circuitry and other materials to prevent fires.
The retardants way of action is complex and depends by the specific nature of the material they are protecting and are made off. For example, the ammonium adheres to the surface of vegetation and can retard the flame, the phosphates can react with some of the active species appeared after combustion and inhibit the propagation of flames, whereas the brominated flame retardants release bromine atoms (free radicals) into the gas phase and reduce the heat generated and slow or prevent the burning process.
Flame retardants and water contamination In the last decade there has been an intense debate about the risk that pose the flame retardants on environment, in general and on aquatic ecosystems, in particular. At the beginning the negative impact on environment of flame retardants was neglected, as their main active ingredients are agricultural fertilizers. However, a compound even if it has low toxicity can cause adverse environmental effects, when there is an intensive use of the product and it is accumulating in water, soil, atmosphere from where they are finally uptake by organisms. The nowadays concern about these contaminants is justified since several of them are corrosive and toxic, have limited biodegradability (as all halogenated organic compounds) being hence highly persistent and tend to accumulate in the environment on long term. The bioaccumulation of flame retardants as any other persistent “anthropogenic” compound is notable in the food chain, being found in zooplankton, invertebrates and fishes (Bayen et al., 2008; Segev et al., 2009). Flame retardants appear not only to be the attribute of human abilities to synthetize chemically these compounds, but can be also produced in nature by organisms. Recently, a group of researchers from the Scripps Institution of Oceanography at the University of California San Diego found a marine sponge that host a bacteria able to produce toxic compounds nearly identical to human-made fire retardants (Agarwal et al., 2017).
Toxicity effect of flame retardants on aquatic organisms The toxicity of flame retardants components on aquatic organisms are due to their inorganic and organic components. Hence, ammonium salts is one of the most toxic compound when it is dissociated to ammonia (a common compound resulted from nitrates reduction by bacteria). The effects of the ammonia further depend by the water temperature and pH since they influence the equilibrium reaction of ammonium-ammonia. Toxicity studies with flame retardants have been mainly performed in laboratory conditions on algae, amphibians and fishes, the later in different development stages (Hamilton et al. 1996; Buhl and Hamilton 1998). These laboratory testing aiming to tests the fishes mortality are of huge help because dose-response studies have significant implications on simulation models developed to estimate the effect of direct delivery of flame retardants on water and organisms mortality. An important direct effect of flame retardants toxicity was detected to be enhanced in the presence the UV-B radiation. The toxicity of the retardant in this case is due to sodium ferrocyanide, a corrosion inhibitor that is toxic for the fish Oncorhynchus mykiss and the frog Rana sphenocephala because it releases cyanides (Little and Calfee 2000). Brominated flame retardants have high acute toxicity to aquatic organisms, such as algae, mollusks, crustaceans and fish and at the cellular level their action has been proved to induce hemocyte lysosomal membrane destabilization (Canesi et al., 2005).
The outdoor testing of flame retardants on fish’s shows that these compounds even when highly diluted is lethal for aquatic organisms (Gaikowski et al. 1996). Changes in the concentration of retardants in streams were detected up to 2.7 km downstream the aerial release and mortality was registered after 1 day. The spills of the flame retardants in streams cause substantial mortality of fishes but this also depends by the stream size, flow rates and type of interstitial riverbed sediments and soil. The soil type and instream sediments have a significant implication on the retention of flame retardants, since there are ions exchanges among soil and the component substances of the retardant. The ash resulted from the fire, at low concentration clogs the fish’s gills and imped the respiration, these having sometimes a similar hazardous effect as the chemical compounds from the retardants.
The side effects of fire-fighting chemicals on wildlife in general and on aquatic organisms in particular are inherent, and it should be considered by fire control managers to protect the biota and their aquatic habitats. Bioremediation process post-fires are the most significant action that managers could take into account rapidly as to eliminate or at least to reduce the flame retardants compounds from the “receiving” environment. Although the bioremediation processes are difficult and complex, the recent studies on biodegradation of flame retardants using microorganisms in both aerobic and anaerobic conditions are promising (Segev et al., 2008). Among them the most effective are dehalogenating bacteria present in groundwater that has been proved to biodegrade during transport in low permeability chalk aquifer (Amon et al., 2005). In the case of in situ groundwater bioremediation, several particularities of the aquifer should be considered such are the physicochemical conditions of the rock and water, residence time of the water and biological factors. Several bioremediation tests have been also performed in reactors with controlled conditions and concentrated biomass acclimated to treat the industrial wastewaters using biological treatment. These test indicates a significant biodegradation of the flame retardant 2,4,6-tribromophenol (TBP) in aerobic conditions. TBP was also conceivable to be biodegraded in anaerobic conditions by bacteria such as Achromobacter piechaudii, Desulfovibrio stain TBP-1 and Ochrobacterium sp. strain TB01.
Since the effects of several flame retardants compound on surface and groundwater aquatic invertebrates is poorly known, the Groundwater Ecology Group from IMDEA Agua aim to design a protocol for testing, evaluating and determination of the sensitivity of surface and typical groundwater invertebrate species to flame retardants compounds recently detected in Spanish waters. We specifically aim to tackle the lethal and sublethal concentrations of selected flame retardant contaminants on surface and groundwater crustacean invertebrates. Our study targets to contribute to current attempts in establishing the effects of flame retardant compounds on aquatic organisms and to advance the assessment ecological risk tools especially in one of the most vulnerable aquatic ecosystem and challenging in terms of remediation – the groundwater.
Acknowledgement: Talent Attraction Program contract no. 2016-T3/AMB-1951. Consejería de Educación, Juventud, y Deporte, Community of Madrid.
Arnon S., A. Eilon, Z. Ronen, A. Nejidat, A. Yakirevich, R. Nativ. 2005. Biodegradation of 2,4,6-Tribromophenol during transport in fractured chalk. Environ. Sci. Technol. 39: 748–755.
Agarwal, V., J.M. Blanton, S. Podell, A. Taton, M.A. Schorn, J. Busch, Z. Lin, E.W. Schmidt, P.R. Jensen, V.J. Paul, J.S. Biggs, J.W. Golden, E.E. Allen, B.S. Moore. Metagenomic discovery of polybrominated diphenyl ether biosynthesis by marine sponges. Nature Chemical Biology, 2017; 13 (5): 537.
Canesi L, Lorusso LC, Ciacci C, Betti M, Gallo G., 2005. Effects of the brominated flame retardant tetrabromobisphenol-A (TBBPA) on cell signaling and function of Mytilus hemocytes: involvement of MAP kinases and protein kinase C. Aquat Toxicol. 75(3):277-87.
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