LEVELS OF NATURAL AND ANTHROPOGENIC RADIONUCLIDES IN SEDIMENTS OF SOME MOROCCAN COASTAL AREAS AND DOSE ASSESSMENT BASED ON ERICA TOOL.

In this work, we considered the concentrations of natural and anthropogenic radionuclides (namely the 40K, 210Pb, 226Ra, 137Cs, 234Th, 228Th and 228Ra) in sediments from Moroccan coast areas by considering estuaries (Sebou and Loukkos) and marine ecosystems (M'diq Bay and three Lagoons: Moulay Bousselham, Sidi Moussa and Oualidia). Sediment samples were analyzed using Gamma spectrometry. The objective was to establish radioactivity levels in Moroccan coastal areas as well as radiological risk assessment by using the ERICA tool. The software allows the estimation of dose rates to biota (a set of reference organisms by default). The highest activity concentrations were found in sediment samples of Sidi Moussa Lagoon, possibly due to the anthropogenic activities, while the lowest levels were reported in Sebou estuary, attributed most probably to a flooding event that occurred in the same year of sampling. Also, 210Pb and 40K have the most significant concentrations, while 137Cs has the lowest concentrations with a great resemblance with similar works. The World Wide Average concentration of 226Ra was exceeded in the three lagoons and that of 40K only exceeded at Sidi Moussa Lagoon. The application of ERICA tool allowed the assessment of total dose rates that are mainly due to internal exposure with strong contribution of 226Ra mainly for phytoplankton in the case of marine ecosystems and insect larvae, mollusc-bivalve, mollusc-gastropod and zooplankton for estuary ecosystems. The total dose rates were far lesser than the admissible dose rate proposed by ERICA tool (10 µGy h-1) and, therefore, unlikely to cause harmful effects to organisms.

Recent pollution records in Sidi Moussa coastal lagoon (western Morocco) inferred from sediment radiometric dating.

The Sidi Moussa lagoon, located in western coastal Morocco and ranked as a wetland of biological and ecological importance (Ramsar site), is contaminated due to its proximity to the industrial phosphate plants and other anthropogenic activities around it. This study was carried out to assess the current environmental state of the lagoon as well as historical inputs of pollutants over several decades. Three sediment cores were collected and analyzed for the determination radionuclide activities (210Pb, 226Ra, 238U and 137Cs) by gamma spectrometry and element concentrations by Inductively Coupled Plasma - Mass Spectrometry. Age-depth relationships were established in two cores using 210Pb and 137Cs as chronometer and time-marker, respectively, and Constant Rate of Supply as radiometric dating model. 210Pb and 238U were present in sediment in activities much higher than those reported for non-contaminated coastal systems. Sediment accumulation rates showed a slight increase over time with a depth-averaged value of 0.16 g cm-2 y-1. Enrichment Factors and practically derived sediment quality guidelines were used to assess sediment contamination/pollution and toxicological effects linked with the measured concentrations of sediment-bound elements. The profiles of Cr, Co, Cu, As and Ni displayed maximums at depths matching the start of the phosphate industrial plants, and decreasing concentrations in the sections above the maximums, revealing the positive effects of the environmental management system adopted by the phosphate company since early 2000s.

From radiometry to chronology of a marine sediment core: A 210Pb dating interlaboratory comparison exercise organised by the IAEA.

Laboratories from 14 countries (with different levels of expertise in radionuclide measurements and 210Pb dating) participated in an interlaboratory comparison exercise (ILC) related to the application of 210Pb sediment dating technique within the framework of the IAEA Coordinated Research Project. The laboratories were provided with samples from a composite sediment core and were required to provide massic activities of several radionuclides and an age versus depth model from the obtained results, using the most suitable 210Pb dating model. Massic concentrations of Zn and Cu were also determined to be used for chronology validation. The ILC results indicated good analytical performances while the dating results didn't demonstrate the same degree of competence in part due to the different experience in dating of the participant laboratories. The ILC exercise enabled evaluation of the difficulties faced by laboratories implementing 210Pb dating methods and identified some limitations in providing reliable chronologies.

Using the radioligand-receptor binding assay for paralytic shellfish toxins: A case study on shellfish from Morocco.

Paralytic shellfish poisoning (PSP) events occur regularly along the Mediterranean and Atlantic coast of Morocco, and have been responsible for several severe cases of human intoxication. Along the southern Atlantic coast of Morocco, aquaculture and intensive artisanal fishing practices have recently been particularly heavily impacted, and toxic species have been observed in increasing intensity and frequency. In the 1990's a regulatory monitoring program was established for the coastal waters off Morocco by the National Institute of Fisheries Research (INRH), to reduce the risk of intoxication with biotoxins. The regulatory monitoring is conducted weekly and includes toxic phytoplankton enumeration and identification, as well as saxitoxin (STX) analysis in seafood using the mouse bioassay (MBA). Animal testing remains the most widely used screening method for PSP toxin detection, yet its use is being reconsidered for animal-related ethical issues, as well as for practical considerations. To be able to better evaluate alternatives to animal testing, the performance of a nuclear-based radioligand-receptor binding assay (RBA) for paralytic shellfish toxins was assessed and compared with the MBA using four commercially important shellfish matrices, including cockles Cerastoderma edule, razor shells Solen marginatus, oysters Crassostrea gigas, and mussels Perna perna. Over 50 samples were collected and analysed as part of the regulatory monitoring framework including a suite of monthly samples from 2017 and all samples identified as toxic by MBA since 2011. Testing of reference material and evaluation of assay-critical parameters (e.g. slope of calibration curve, internal quality control QC and IC50) confirmed the robustness of the RBA methodology. With this RBA method, STX-like activity detected in shellfish samples ranged from 33 to 8500 µg STX equivalents per kg. RBA data were significantly correlated (P < 0.0001, Pearson r = 0.96) with the MBA-derived dataset. Importantly, the RBA method allowed for the detection and quantification of PSP toxins at levels not detectable by using the mouse bioassay. The limits of quantification of the RBA was calculated and found to be 10-fold lower than that of the MBA, respectively 35.24 ±â€¯5.99 and 325 µg STX equivalents per kg of tissue. In addition, the RBA was easier to use and produced reliable results more rapidly than the MBA and without use of live animals. Considering the increasing risks associated with harmful algal blooms, globally and in Morocco, together with the increased development of aquaculture production and seafood consumption and the difficulties of live animal testing, these findings indicate that the RBA method is a reliable and effective alternative to the MBA method.

Radioecological assessment and radiometric dating of sediment cores from dynamic sedimentary systems of Pra and Volta estuaries (Ghana) along the Equatorial Atlantic.

The Volta and Pra estuaries (Ghana, West Africa) are dynamical sedimentary systems whose natural equilibrium is being affected by anthropogenic activities. This paper reports depth-distributions of 210Pb, 226Ra, 234Th, 40K, 228Ra and 137Cs for two sediment cores from these estuaries. Bulk densities were not steady-state and well correlated with 40K (p < 0.00005). Unsupported 210Pb profiles were incomplete, non-monotonic and showed large fluctuations. The assumptions involved in the common 210Pb-based dating models were not meet in these dynamical scenarios, and the use of 137Cs as a time-marker is difficult in Equatorial and South-Hemisphere countries due to its low fallout rates. Chronologies have been solved with the new 210Pb-based TERESA model, which operates with varying but statistically correlated fluxes and sediment accumulation rates (SAR). The core from the Volta reflects the conditions prevailing after the construction of the Akosombo Dam, with a mean SAR of 1.05 ± 0.03 g cm-2·y-1, while a higher value of 2.73 ± 0.06 g cm-2·y-1 was found in the Pra, affected by intense gold mining activities along its course. Radiological and radioecological assessments have been conducted by applying the UNSCEAR protocols and the ERICA model, respectively. The measured radionuclide concentrations do not pose any significant risk for the environment and human health.

Radionuclide activities and metal concentrations in sediments of the Sebou Estuary, NW Morocco, following a flooding event.

This study presents metal concentrations (Fe, Mg, Mn, Co, Cu, Zn, Pb, As, Sr and V) and radionuclide activities ((40)K, (137)Cs, (210)Pb, (226)Ra, (228)Ac, (234)Th and (212)Pb) in surface deposits and a sediment core from the Sebou Estuary, Northwest Morocco. Samples were collected in April 2009, about 2 months after a flooding event, and analysed using a well-type coaxial gamma-ray detector and inductively coupled plasma-quadrupole mass spectrometry. Activities of radionuclides and concentrations of almost all elements in surface samples displayed only moderate spatial variation, suggesting homogenous deposition of eroded local soil in response to intense precipitation. Excess (210)Pb displayed relatively constant activity throughout the sediment core, preventing dating and precluding determination of the historical accumulation rates of pollutants at the core site. Some elements showed non-systematic trends with depth and displayed local maxima and minima. Other elements presented relatively systematic concentration trends or relatively constant levels with discrete maxima and/or minima. Except for Mn, Sr and Cr, all metal concentrations in sediment were below levels typical of polluted systems, suggesting little human impact or losses of metals from sediment particles.

Partitioning of radiostrontium in marine aqueous suspensions: laboratory experiments and modeling studies.

Quantitative information on the adsorption/desorption of radionuclides by suspended loads is important in the study of their environmental behavior. In this paper, controlled laboratory experiments were directed at studying the kinetic transfer and final distribution of radiostrontium in aqueous suspensions using 85Sr as tracer. The results showed that the uptake of 85Sr in seawater can be properly described by one reversible-reaction model. However, in the absence of competitive cations, it has been shown that two reactions of different characteristic times are unambiguously involved in the kinetic evolution of adsorption. Thus, a modeling approach consisting of three-box model has been applied. The model predicts in a satisfactory way the time evolution of activities in the dissolved phase and two sites in the particles. Experimental evidence showed, through comparison among kinetic and distribution coefficients corresponding to different conditions, that Ca2+ affects strongly the rate and extent of Sr uptake by suspended particles. On the other hand, distribution coefficients were found to be sensitive to changes in suspended particulate matter (SPM) concentration, exhibiting a reverse effect with this parameter on the adsorption. In addition, desorption from particles is important showing that Sr can be easily released due to cation-exchange processes.

Trends of radionuclide sorption by estuarine sediments. Experimental studies using 133Ba as a tracer.

Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced 226Ra concentrations. 133Ba was used as a tracer since it is a gamma emitter and a good analogue of the environmental behaviour of 226Ra. Laboratory experiments have been carried out to quantify the uptake kinetics of 133Ba by sediments in aqueous suspensions and by sediment cores under a water column at rest. Depth distributions of 133Ba in sediments have been studied with different contact times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l(-1) suspension) and sediment cores (up to 70% in a few minutes). The kinetics of the uptake by suspended sediments could be reasonably described by a model of two parallel and reversible reactions followed by a weakly-reversible reaction. The total uptake and the rate of reaction decreased with the increment of grain size. Furthermore, uptake following diffusion through the interstitial water was hardly detectable beyond 1 cm depth. For the case with more experimental results, the depth distribution could be reasonably described by the analytical solution based on the use of an effective diffusion coefficient (4.2 x 10(-12) m2 s(-1)) and the measured intrinsic distribution coefficient (kd = 63 +/- 6 l kg(-1)).