Mercury bioaccumulation in the spotted dogfish (Scyliorhinus canicula) from the Atlantic Ocean

The annual and life-cycle mercury bioaccumulation pattern in selected tissues of the economically relevant Elasmobranchii species Scyliorhinus canicula was studied, and the risks associated with its consumption evaluated.Preferential mercury bioaccumulation occurred in muscle tissue, and followed the order muscle > heart > liver > gills > pancreas. Total mercury in muscle tissue ranged from 0.13 mg kg⁻¹ (wwt) in 1+ year old males to 0.8 mg kg⁻¹ (wwt) in 8+ year old mature females, with no significant differences found between genders, and no clear lifespan bioaccumulation pattern observed, except for mature females. Organic mercury in the muscle ranged from 0.05 mg kg⁻¹ (wwt) to 0.52 mg kg⁻¹ (wwt), corresponding to an average of 70% of total mercury content. In mature females, a significant correlation (R = 0.99, P = 0.01) was found between size and organic mercury fraction, suggesting reproduction as an important factor controlling organic mercury bioaccumulation in the spotted dogfish.     

Inorganic and methylmercury: do they transfer along a tropical coastal food web?

Methylmercury (MeHg) and inorganic mercury (Hg_inorg) were evaluated in the water of a Brazilian estuary, with two size classes of plankton and seven fish species of different feeding habits. Water partition coefficients (PCs) in microplankton were fourfold higher for MeHg than for Hg_inorg; and water PCs in mesoplankton were 26 times higher for MeHg than Hg_inorg. Difference between microplankton and mesoplankton MeHg bioaccumulation factor (BAF) was higher (0.60 log units) than Hg_inorg BAF (0.24 log units), indicating that trophic transfer of MeHg between planktonic organisms is more efficient than Hg_inorg transference. MeHg concentrations, proportion of mercury as MeHg and its biotransference factors (BTFs) in the microplankton, mesoplankton and fish increased with increasing trophic level while biotic concentrations of Hg_inorg and proportion of mercury as Hg_inorg decreased thus indicating that MeHg was indeed the biomagnified species of mercury. MeHg reflected the vertical trophic guilds distribution, due to the fact that the top predator fish presented the highest concentration (0.77 μg g⁻¹ d.w.), followed by the less voracious species (0.43 μg g⁻¹ d.w.); while planktivorous fish presented the lowest concentrations (0.044 μg g⁻¹ d.w.). Hg_inorg did not present the same behavior. Results suggest that feeding habits and trophic guild are important parameters, influencing biotransference and biomagnification processes.     

Critical erosion profiles in macro-tidal estuary sediments: Implications for the stability of intertidal mud and the slope of mud banks

Vertical profiles of the critical erosion threshold (τ_crit) in sediment have been measured at 11 stations along the axis of the Tamar Estuary and at a single station in a tributary of the Tamar at St. John's Ford. The τ_crit of surface sediment increased from 0.04 Pa in the upper, brackish estuary to 0.09 Pa in the lower estuary. In the upper estuary τ_crit only increased slightly with depth whereas in the marine estuary τ_crit increased rapidly from 0.09 Pa at the surface to 0.25 Pa at 15 cm below the sediment surface. The results showed that the relationship between τ_crit and bulk density (ρ_b) obtained previously for surface sediment was also applicable to sediments from depths of 10–15 cm and probably deeper. Profiles of ρ_b were measured to depths of 70 cm using a corer. In the lower (marine) estuary ρ_b increased with depth in the sediment from 1580 kg m⁻³ at the surface to 1720 kg m⁻³ at 70 cm. In the upper estuary ρ_b values were lower at 1170–1200 kg m⁻³ and profiles were almost homogeneous indicating that consolidation was not occurring. The mid-estuary was transitional between these two situations. These results are consistent with the seasonal accumulation and loss of ‘mobile’ sediment observed previously in the upper estuary with changes in river flow, and with the apparent stability of intertidal mud in the lower marine estuary deduced from historical bathymetric survey records. The slopes of the intertidal mud banks ranged from 1–2% in the lower estuary to 20–25% in mid-estuary but, instead of continuing to increase in steepness towards the head as the estuary became narrower, the measured slopes actually decreased. It is speculated that the lack of consolidation through continual mobilisation and settlement cycles combined with an increase in silt content in the upper estuary resulted in sediment that lacked the mechanical strength to maintain steep slopes.     

Levels and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments from Lenga Estuary, central Chile

The Lenga Estuary is a small brackish wetland located southwest of San Vicente Bay, Region VIII, Chile. Surface sediment from nine sites in the estuary were analysed for PAHs and compared to Sediment Quality Guidelines (SQG). Sediment samples were freeze dried and soxhlet extracted for 16 h using DCM. Identification and quantification was carried out by HPLC. Organic carbon was also determined. Results showed total PAH concentrations ranged from 290 to 6118 (2025 ± 1975) ng g⁻¹ d.w. (2025 ± 1975). Results for organic carbon percentages ranged from 1% to 7%. Statistical analysis showed a significant positive correlation (Pearson test) between organic carbon percentage PAHs. Comparison of contaminant levels and international Sediment Quality Guidelines (SQG) (ERL and ER) suggested that sediment of the Lenga estuary did not show any ecotoxicologial risk for benthic organisms where high levels of PAHs were detected. Monitoring of this and other contaminants is recommended in Chile.     

Effects of an estuarine plume-associated bloom on the carbonate system in the lower reaches of the Pearl River estuary and the coastal zone of the northern South China Sea

We observed a phytoplankton bloom downstream of a large estuarine plume induced by heavy precipitation during a cruise conducted in the Pearl River estuary and the northern South China Sea in May–June 2001. The plume delivered a significant amount of nutrients into the estuary and the adjacent coastal region, and enhanced stratification stimulating a phytoplankton bloom in the region near and offshore of Hong Kong. A several fold increase (0.2–1.8 μg Chl L⁻¹) in biomass (Chl a) was observed during the bloom. During the bloom event, the surface water phytoplankton community structure significantly shifted from a pico-phytoplankton dominated community to one dominated by micro-phytoplankton (>20 μm). In addition to increased Chl a, we observed a significant drawdown of pCO₂, biological uptake of dissolved inorganic carbon (DIC) and an associated enhancement of dissolved oxygen and pH, demonstrating enhanced photosynthesis during the bloom. During the bloom, we estimated a net DIC drawdown of 100–150 μmol kg⁻¹ and a TAlk increase of 0–50 μmol kg⁻¹. The mean sea–air CO₂ flux at the peak of the bloom was estimated to be as high as ∼−18 mmol m⁻² d⁻¹. For an average surface water depth of 5 m, a very high apparent biological CO₂ consumption rate of 70–110 mmol m⁻² d⁻¹ was estimated. This value is 2–6 times higher than the estimated air–sea exchange rate.     

Selenium in sediments and biota from estuaries of southwest England

Selenium concentrations have been measured in sediment, fucoid macroalgae and macroinvertebrates from four estuaries of SW England (Yealm, Plym, Looe, Fal). Sediment concentrations ranged from about 0.4 μg g⁻¹ in the Yealm to 1.49 μg g⁻¹ at one site in the Plym. Concentrations in Fucus vesiculosus (0.05–0.31 μg g⁻¹) and F. ceranoides (0.05–0.51 μg g⁻¹) were significantly lower than corresponding concentrations in sediment but there was no correlation between algal and sediment concentrations. Selenium concentrations in Littorina littorea (∼4 μg g⁻¹), Hediste diversicolor (2.82–12.68 μg g⁻¹), Arenicola marina (∼17 μg g⁻¹) and Scrobicularia plana (1.18–6.85 μg g⁻¹) were considerably higher than concentrations in macroalga or sediment, suggesting that Se is effectively accumulated from the diet. Although Se concentrations in some invertebrates exceed toxicity thresholds for the diet of predacious birds and fish, no specific evidence for Se toxicity exists in these estuaries.     

Effects of low tide rainfall on the erodibility of intertidal cohesive sediments

Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min⁻¹ for 6 min) and low (0.36 mm min⁻¹ for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s⁻¹ (ME-30, g m⁻²) and critical erosion velocity (U_crit, m s⁻¹)) were determined in annular flumes (bed area=0.17 m²). Ambient/control sediment erodibility in May (ME-30=211 g m⁻², U_crit=0.18 m s⁻¹) was higher than in August (ME-30=30 g m⁻², U_crit=0.26 m s⁻¹) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m⁻²) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm⁻²). In contrast, in August H. ulvae densities were low (52 ind. m⁻²) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm⁻²). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in U_crit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, U_crit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability.     

Distributions of polycyclic aromatic hydrocarbons in the Daliao River Estuary of Liaodong Bay, Bohai Sea (China)

The distributions of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the aqueous phase, suspended particulate matter (SPM), sediment, and pore water of the Daliao River Estuary in Liaodong Bay, Bohai Sea (China). Total PAH concentrations ranged from 139.16 to 1717.87 ng L⁻¹ in surface water, from 226.57 to 1404.85 ng L⁻¹ dry weight in SPM, from 276.26 to 1606.89 ng g⁻¹ dry weight in sediments, and from 10.20 to 47.27 μg L⁻¹ in pore water. PAH concentrations were at relatively moderate levels in water, SPM, sediment and pore water in comparison with those reported for other estuary and marine systems around the world. Sedimentary PAH concentrations decreased offshore owing to active deposition of laterally-transported river-borne particles. PCA analysis of the possible PAH source suggested petrogenic and pyrolytic PAH inputs in the studied region.     

Seasonal variations in the inorganic carbon system in the Pearl River (Zhujiang) estuary

Seasonal variations in the inorganic carbon system in the Pearl River estuary are examined based on data from five surveys during the spring, summer, fall, and winter seasons. Both total dissolved inorganic carbon (DIC) and total alkalinity (TAlk) values in the freshwater end-members are high in the dry season (>2700 μmol kg⁻¹ for DIC and >2400 μmol kg⁻¹ for TAlk) and substantially lower in the wet season (DIC and TAlk were ∼1000 and 700 μmol kg⁻¹, respectively). Riverine DIC flux and drainage basin weathering rates, however, are significantly higher in the wet season (611×10⁹ mol yr⁻¹ and 13.6×10⁵ mol km⁻² yr⁻¹) than in the dry season (237×10⁹ mol yr⁻¹ and 5.3×10⁵ mol km⁻² yr⁻¹).     

Seasonal contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m⁻² d⁻¹, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (C_phyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m⁻² d⁻¹ and 22 mg chl a m⁻² d⁻¹, respectively) and minimum values during winter (22 mg m⁻² d⁻¹ and 0.1 mg chl a m⁻² d⁻¹, respectively). The contribution of C_phyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of C_phyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, C_phyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal C_phyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.     

What drives the evolution of the sedimentary phosphorus cycle?

The ‘Chicken Creek’ artificial catchment area, Welzow-South, E Germany, created to study processes and structures of initial ecosystem development, discharges into a small experimental lake (A=3805 m², V=3992 m³, z_max=2.4 m). This lake was man-made in 2005 and filled by natural surface runoff until January 2006. In summer 2006 and 2008, the actual development of sediments and the evolution of the phosphorus (P) cycle were studied. 19.7% of the original lake volume was filled by sediment within the first 3 years. A fine-grained sediment representing silt (6.3-63 μm) accumulated at high accretion rates at the deepest point (200 mm a⁻¹, 0-24 mm week⁻¹) due to massive erosion in the catchment. The sediment is low in organic matter (2.5-5.2%) and total P (TP, 0.31-0.97 mg g⁻¹). Low amounts of P associated with degradable organic matter and surplus of metal hydroxides (Fe:P∼40, Al:P∼20) favor an efficient P binding and low dissolved P concentrations in pore water (1-107 μg l⁻¹). Hence, the mineral sediment quality and the low rates of P release (0.06 mg m⁻² d⁻¹) revealed that a lake at an initial stage of development has essentially no sedimentary P cycle compared to eutrophic shallow lakes. However, the increasing emersed and submersed macrophyte growth will control further lake succession by intensifying the internal nutrient cycling. The macrophytes drive the evolution of a sedimentary P cycle by mobilizing and translocating P, by accumulating carbon and thus by stimulating microbial and redox processes.     

A trophic model for the Danshuei River Estuary, a hypoxic estuary in northern Taiwan

The estuary of the Danshuei River, a hypoxic subtropical estuary, receives a high rate of untreated sewage effluent. The Ecopath with Ecosim software system was used to construct a mass-balanced trophic model for the estuary, and network analysis was used to characterize the structure and matter flow in the food web. The estuary model was comprised of 16 compartments, and the trophic levels varied from 1.0 for primary producers and detritus to 3.0 for carnivorous and piscivorous fishes. The large organic nutrient loading from the upper reaches has resulted in detritivory being more important than herbivory in the food web. The food-chain length of the estuary was relatively short when compared with other tropical/subtropical coastal systems. The shortness of food-chain length in the estuary could be attributed to the low biomass of the top predators. Consequently, the trophic efficiencies declined sharply for higher trophic levels due to low fractions of flows to the top predators and then high fractions to detritus. The low biomass of the top predators in the estuary was likely subject to over-exploitation and/or hypoxic water. Summation of individual rate measurements for primary production and respiration yielded an estimate of −1791 g WW m⁻² year⁻¹, or −95 g C m⁻² year⁻¹, suggesting a heterotrophic ecosystem, which implies that more organic matter was consumed than was produced in the estuary.     

Organohalogen contaminants and trace metals in North-East Atlantic porbeagle shark (Lamna nasus)

The North-East Atlantic porbeagle (Lamna nasus) population has declined dramatically over the last few decades and is currently classified as ‘Critically Endangered’. As long-lived, apex predators, they may be vulnerable to bioaccumulation of contaminants. In this study organohalogen compounds and trace elements were analysed in 12 specimens caught as incidental bycatch in commercial gillnet fisheries in the Celtic Sea in 2011. Levels of organohalogen contaminants were low or undetectable (summed CB and BDE concentrations 0.04–0.85 mg kg⁻¹ wet weight). A notably high Cd concentration (7.2 mg kg⁻¹ wet weight) was observed in one mature male, whereas the range observed in the other samples was much lower (0.04–0.26 mg kg⁻¹ wet weight). Hg and Pb concentrations were detected only in single animals, at 0.34 and 0.08 mg kg⁻¹ wet weight, respectively. These contaminant levels were low in comparison to other published studies for shark species.     

Matrix-bound phosphine in sediments from Lake Illawarra, New South Wales, Australia

Matrix-bound phosphine (MBP) has been measured in sediment from two cores in Lake Illawarra on the south east coast of Australia. The sediments were also dated in the upper layers. MBP concentrations found range from 142 to 1813 ng kg⁻¹, dw (dry weight of sediment) with some values being amongst the highest ever measured. Values of MBP in deeper sediments were higher than for near surface samples, but the patterns with depth were not consistent. Strong correlations were noted between MBP and organic phosphorus (OP, r > 0.8) and with total phosphorus (TP, r > 0.7), but only moderate correlations were found with organic carbon (OC, r > 0.5). No correlations were found between MBP concentrations and the age of the sediments. It was confirmed that high MBP concentrations are indicative of a phosphorus rich environment. The results tend to support the premise that MBP is generated by microbial attack on OP under anaerobic conditions.     

Levels of Po and Pb in mussel and sediments in Candarlı Gulf and the related dose assessment to the coastal population

²¹⁰Po and ²¹⁰Pb in mussel (Mytilus galloprovincialis) and sediment samples collected at Candarl? Gulf during the period of 2010–2012 are presented and discussed. The activity concentrations of ²¹⁰Po and ²¹⁰Pb were measured by means of alpha spectrometry. Activity concentrations of ²¹⁰Po and ²¹⁰Pb in mussels are in the ranged of 332 ± 17–776 ± 23 Bq kg⁻¹ dw and 14 ± 1–40 ± 5 Bq kg⁻¹ dw, for sediments the ranges for 52 ± 5–109 ± 8 Bq kg⁻¹ dw and 38 ± 5–92 ± 9 Bq kg⁻¹ dw, respectively. The estimated consequent annual effective ingestion dose due to ²¹⁰Po and ²¹⁰Pb from mussel consumption in Candarl? Gulf coastal region were calculated. The highest dose due to ²¹⁰Po and ²¹⁰Po were calculated to be 4232 ± 126 μSv and 126 ± 16 μSv, respectively.     

Spartina densiflora demonstrates high tolerance to phenanthrene in soil and reduces it concentration

The present study was conducted to investigate the tolerance of Spartina densiflora to phenanthrene, and to test its ability in phenanthrene dissipation. A glasshouse experiment was designed to investigate the effect of phenanthrene from 0 to 1000 mg kg⁻¹ on growth and photosynthetic apparatus of S. densiflora by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigments. We also performed chemical analysis of plant samples, and determined the concentration of phenanthrene remaining in soil. S. densiflora survived to concentrations as high as 1000 mg kg⁻¹ phenanthrene in soil; in fact, there was no significant difference in RGR among the treatments after 30 days. Otherwise, phenanthrene affected photosynthetic apparatus at 100 and 1000 mg kg⁻¹; thus, the lower Φ_PSII could be explained by the declined photosynthetic pigment concentrations. Soil extraction indicated a more marked rate of phenanthrene disappearance in the soil in the presence of S. densiflora.     

Relationship of photosynthetic carbon fixation with environmental changes in the Jiulong River estuary of the South China Sea, with special reference to the effects of solar UV radiation

Phytoplankton cells in estuary waters usually experience drastic changes in chemical and physical environments due to mixing of fresh and seawaters. In order to see their photosynthetic performance in such dynamic waters, we measured the photosynthetic carbon fixation by natural phytoplankton assemblages in the Jiulong River estuary of the South China Sea during April 24-26 and July 24-26 of 2008, and investigated its relationship with environmental changes in the presence or the absence of UV radiation. Phytoplankton biomass (Chl a) decreased sharply from the river-mouth to seawards (17.3-2.1 μg L⁻¹), with the dominant species changed from chlorophytes to diatoms. The photosynthetic rate based on Chl a at noon time under PAR-alone increased from 1.9 μg C (μg Chl a)⁻¹ L⁻¹ in low salinity zone (SSS < 10) to 12.4 μg C (μg Chl a)⁻¹ L⁻¹ in turbidity front (SSS within 10-20), and then decreased to 2.1 μg C (μg Chl a)⁻¹ L⁻¹ in mixohaline zone (SSS > 20); accordingly, the carbon fixation per volume of seawater increased from 12.8 to 149 μg C L⁻¹ h⁻¹, and decreased to 14.3 μg C L⁻¹ h⁻¹. Solar UVR caused the inhibition of carbon fixation in surface water of all the investigated zones, by 39% in turbidity area and 7-10% in freshwater or mixohaline zones. In the turbidity zone, higher availability of CO₂ could have enhanced the photosynthetic performance; while osmotic stress might be responsible for the higher sensitivity of phytoplankton assemblages to solar UV radiation.     

Allometric relationships of Po and Pb in mussels and their application to environmental monitoring

Mussels from the Portuguese coast collected during several seasons of the year have shown ²¹⁰Po and ²¹⁰Pb body burdens (Bq mussel⁻¹) that increased with mussels’ body size but displayed significant decrease in radionuclide concentrations (Bq kg⁻¹). For example, the increase of mussel size from 2.5 cm to 5.0 cm maximum shell length corresponded in average to a 50% decrease of ²¹⁰Po activity concentration in soft tissues from 1065 Bq kg⁻¹ (dw) to 540 Bq kg⁻¹ (dw). A similar reduction in concentration was observed for ²¹⁰Pb. The physiological condition of mussels, relating to fat and glycogen storage, had an effect on radionuclide concentrations, although the total body burden of radionuclide in mussels remained nearly constant throughout the year. These factors may play an important role in data interpretation for environmental monitoring programmes. Besides the mussel size and condition index, due to the inter-individual variation even inside narrow mussel size classes, the sample size, i.e., the number of specimens in one mussel sample is another key factor to be considered when obtaining environmentally representative radionuclide concentrations.     

Source apportionment of sedimentary hydrocarbons in the Segara Anakan Nature Reserve,Indonesia

The study aimed to determine the spatial distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in surface sediments of the Segara Anakan nature reserve and their potential origins using gas chromatography–mass spectrometry. Total alkane concentrations ranged from 3755 to 129,027 μg kg⁻¹, and the concentrations of 16 PAHs ranged from 375 to 29,517 μg kg⁻¹. The ratios of specific n-alkanes (e.g., CPI_24–34, WaxC_n, and Paq), including a new proposed index, terrestrial–marine discriminant (TMD), as well as the ratios of selected PAHs (e.g., Ant/∑178, Fl/∑202, BaAnt/∑228, and IPyr/∑276), showed that the sources of hydrocarbons in the sediments were generally biogenic, including both terrigenous and marine, with an anthropogenic pyrolytic contribution (petrogenic and biogenic combustion). For the environmental risk assessment, a sediment quality guideline (SQGs) comparison indicated that the station risk levels ranged from low to medium-low, except for R6, which has a greater impact on the ecological risk for marine organisms.