Paper: Castro-Jiménez, J.; Berrojalbiz, N.; Pizarro, M.; Dachs, J. Organophosphate ester (OPE) flame retardants and plasticizers in the open Mediterranean and Black Seas Atmosphere. Environ. Sci. Technol. 2014. DOI: 10.1021/es405337g
They’re in couches, carpets, vehicle upholstery, seat cushions, children’s toys, electrical equipment, and myriad other products: organophosphate esters (OPEs) are widely used as flame retardants (intended to slow the ignitability of furniture and textiles) and plasticizers (used to make plastics more malleable). OPEs are great for these applications because they’re very stable – they don’t break down or thermally degrade easily, so they can slow combustion. Unfortunately, their stability also means they can persist and bioaccumulate after they’re released into the environment. This is particularly worrying because some OPEs are carcinogenic and neurotoxic.
The usage of OPEs has increased in recent years, especially since another group of persistent flame retardants, PBDEs, were banned by the Stockholm Convention in 2009. Since then, studies have reported that OPEs are ubiquitous in the atmosphere – they’ve been found all over the world, even in remote locations. However, concentrations of OPEs had never been measured over the Mediterranean and Black Seas, a densely populated region where high concentrations of other pollutants have been measured.
The atmosphere is a very important source of pollution to semi-enclosed seas and lakes because many compounds can travel long distances in the air and deposit in relatively remote surface waters. To investigate whether OPEs are entering the Mediterranean and Black Seas from the air, and whether they might negatively impact organisms in the water, scientists measured several common OPEs in the atmosphere over the seas.
Scientists from Barcelona, Spain collected samples of atmospheric aerosol during two cruises aboard the R/V Garcia del Cid. The term aerosol refers to tiny solid particles in air that can travel with the wind for long periods of time before depositing onto land or water. Large hydrophobic molecules like OPEs are often released into the atmosphere as individual molecules but later stick onto or absorb into these aerosol particles and accumulate there, much like they stick to sediments and sink to the seafloor. When the aerosol is deposited in the water, it brings pollutants along with it. Scientists have identified this process, called dry deposition, as a major source of pollutants in water bodies like the Mediterranean and the Great Lakes, as well as the open ocean.
The authors found that several OPEs were widespread in the study region – 8 different compounds were found in more than half of the samples. The concentrations of three chlorinated OPEs, known to be the most toxic of the group, are shown in Figure 1.
Researchers used sophisticated atmospheric modeling techniques to calculate “back trajectories” (paths showing where air masses came from before they arrived at the sampling site). Using this method, they determined that air at the sites with highest concentrations seemed to originate from the Aegean Sea and Istanbul as well as Alexandria, indicating that these areas could be significant sources of pollution to the seas.
How much of these compounds are entering the seas?
To get an idea of the total amount of OPEs that could be deposited into the seas in a year, the authors used their measured concentrations to calculate input fluxes. They estimated that the open waters of the Mediterranean receive 13 – 260 tons of OPEs per year, while the Black Sea receives 50 – 170 tons of OPEs. Often in oceanography, scientists have to make these wide-range ballpark estimates to get an idea of how fluxes of compounds could affect natural processes over vast areas.
OPEs as a source of nutrients
OPEs are unique compared to other flame retardants because they contain phosphorous, which is an important nutrient for phytoplankton and microbes. In many cases, phosphorous is a limiting nutrient which means that the amount of bioavailable (able to be broken down and used by organisms) phosphorous dictates the amount of life that can be supported. Scientists are especially concerned with nutrients added by human activities because it can lead to problems like eutrophication, which leads to algal blooms and hypoxia, and disrupts the natural cycle of marine carbon fixation and storage.
While the above calculations are just approximations based on initial measurements, scientists can use these numbers to get some idea of whether OPE deposition could significantly affect marine life in the Mediterranean and Black Seas. The authors theorize that OPEs could indeed be a significant source of phosphorous to marine life, in which case deposition of OPEs could perturb the marine carbon cycle by encouraging increased microbial activity. At this time, however, scientists don’t know whether OPEs are bioavailable to microbes.
This study provided the first measurements of OPE flame retardants in this highly impacted region. It is crucial that researchers gather data on levels of pollutants like OPEs that are currently being used in high volumes so that we can better understand where they end up in the environment and what regions are most likely to be impacted. Now that measurements for this region exist, scientists can compare these “baseline” concentrations with results from future cruises to find out whether levels are decreasing or increasing over time in response to changing usage patterns or regulation of OPEs.