The role of afforestation species as a driver of Hg accumulation in organic horizons of forest soils from a Mediterranean mountain area in SW Europe.

Forest areas are a primary sink of atmospheric mercury (Hg) within terrestrial ecosystems, whereas forest vegetation plays a key role in atmospheric Hg transfer to soil horizons. This study assessed variations in total Hg contents (HgT) and accumulation (HgRes) in the soil organic horizons of a forest area in NE Portugal, where post-wildfire afforestation led to the substitution of the native deciduous species (Quercus pyrenaica) by fast-growing coniferous species (Pseudotsuga menziesii and Pinus nigra). The study also evaluated, for each species, the links between Hg contents and other biophilic elements of soil organic matter (C, N, S) present in organic subhorizons (OL, OF, OH). Mean HgT in the organic horizons of the different tree species follow the sequence: P. nigra (88 µg kg-1) < Q.pyrenaica (101 µg kg-1)

Environmental relevance of adsorption of doxycycline, enrofloxacin, and sulfamethoxypyridazine before and after the removal of organic matter from soils.

In this work batch-type experiments were used to study the adsorption of the antibiotics doxycycline (DC), enrofloxacin (ENR), and sulfamethoxypyridazine (SMP) in cultivation soils, before and after the removal of soil organic matter. Organic matter removal by calcination resulted not only in C and N removal, but also in increased soil pH, exchangeable basic cations and surface area values. The results indicate a very different behavior depending on the type of antibiotic, showing the adsorption sequence DC > ENR > SMP. Specifically, DC adsorption was very high in untreated soil samples (with organic matter), and was still high (although decreased) after the removal of soil organic matter. Furthermore, the adsorption behavior of DC was clearly dependent on the pH of the medium. Regarding ENR, it also showed high adsorption, although to a lesser extent than DC. However, when soil organic matter was removed, ENR adsorption significantly decreased in all soil samples. As regards SMP, it was adsorbed to a much lesser extent, and the removal of soil organic matter caused an additional drastic decrease in adsorption, reaching negligible values in some samples. Desorption followed the reverse sequence of adsorption, specifically in the order DC < ENR < SMP. In the case of DC, desorption was negligible, both in samples with and without organic matter, while for ENR and SMP, desorption clearly increased for soil samples where organic matter was removed. These results may be of relevance as regards environmental quality and public health, especially to facilitate a correct use of soils and organic amendments in areas that receive the application of substances containing the investigated antibiotics.

Sulfadiazine, sulfamethazine and sulfachloropyridazine removal using three different porous materials: Pine bark, "oak ash" and mussel shell.

This work focuses on studying the efficacy of three different by-products to adsorb three antibiotics (sulfadiazine, SDZ; sulfamethazine, SMT; sulfachloropyridazine, SCP). These antibiotics can be considered pollutants of the environment when they reach water, as well as in cases where they are spread on soils through irrigation or contained in sewage sludge or livestock manure. In this study, batch-type adsorption/desorption experiments were performed for each of the three sulfonamides, adding 7 different concentrations of the antibiotics, going from 1 to 50 µmol L-1, and with contact time of 24 h. The results indicate that pine bark is the most efficient bioadsorbent among those studied, as it adsorbs up to 95% of the antibiotics added, while desorption is always less than 11%. However, for "oak ash" and mussel shell the adsorption is always lower than 45 and 15%, respectively, and desorption is high, reaching up to 49% from "oak ash" and up to 81% from mussel shell. Adsorption data showed good fitting to the Linear and Freundlich models, with R2 values between 0.98 and 1.00 in both cases. Kd and KF adsorption parameters showed similar values for the same sorbent materials but were much higher for pine bark than for the other two bioadsorbents. The Freundlich's n parameter showed values in the range 0.81-1.28. The highest KF values (and therefore the highest adsorption capacities) were obtained for the antibiotic SCP in pine bark. Pine bark showed the highest capacity to adsorb each of the antibiotics, increasing as a function of the concentration added. When the concentration of sulfonamide added was 50 µM, the amounts adsorbed were 780 µmol kg-1 for SDZ, 890 µmol kg-1 for SMT, and 870 µmol kg-1 for SCP. "Oak ash" and mussel shell have low adsorption capacity for all three sulfonamides, showing values always lower than 150 µmol kg-1 (oak ash) and 20 µmol kg-1 (mussel shell) when a concentration of 50 µmol L-1 of antibiotic is added. The results of this study could aid to make an appropriate management of the by-products studied, in order to facilitate their valorization and recycling in the treatment of environmental compartments polluted with sulfonamide antibiotics.

Sulfadiazine removal using green zero-valent iron nanoparticles: A low-cost and eco-friendly alternative technology for water remediation.

In this work, the effectiveness of green zero-valent iron nanoparticles (gnZVIs) for the removal of the antibiotic sulfadiazine (SDZ) from water via adsorption and reduction was tested. Additionally, the effectiveness of this material as a catalyst for the Fenton and photo-Fenton processes was also investigated. This represents the first study concerning the use of gnZVIs for the degradation of a sulfonamide antibiotic. The results obtained indicate that gnZVIs were able to remove up to 58% of SDZ via adsorption and up to 69% via adsorption plus reduction using a SDZ/Fe3+ molar ratio of 1:61.6. Furthermore, gnZVIs showed strong effectiveness as a catalyst for the Fenton and photo-Fenton reactions, with complete SDZ removal in 8 h and 5 min, respectively, using a SDZ/Fe3+/H2O2 molar ratio of 1:38.4:38.4. These results demonstrate that the use of gnZVIs constitutes an attractive and potential alternative technology for water remediation, reducing environmental impact and operational costs.

Single and simultaneous adsorption of three sulfonamides in agricultural soils: Effects of pH and organic matter content.

Veterinary antibiotics reaching the environment have become a matter of global concern, since they can cause serious negative impacts on human and ecological health. Therefore, a deep understanding of their behavior and fate once they reach the soil environment is of utmost importance to design and implement appropriate measures that could reduce their potential risks. With this aim, batch-type experiments were carried out to study competitive adsorption and desorption for three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) in six crop soils presenting different characteristics. The results obtained showed that sulfonamides have a low retention in soils, with average adsorption percentages of 40% for SDZ, 44% for SMT and 54% for SCP, and with desorption percentages up to 36% for SDZ and SCP and up to 29% for SMT. The retention of sulfonamides was strongly influenced by the soil organic carbon content (SOC), with higher adsorption and less desorption associated to higher SOC contents. In addition, the hydrophobicity of sulfonamides also had an influence, as higher hydrophobicity resulted in higher affinity for soils, showing the affinity sequences: SDZ ~ SMT

Use of biomass ash to reduce toxicity affecting soil bacterial community growth due to tetracycline antibiotics.

Tetracycline antibiotics (TA) used in veterinary medicine reach terrestrial ecosystems mostly via the repeated applications of animal manures and slurries on agricultural soils, where they may cause toxic effects on bacterial communities. In the current work, we studied the efficacy of adding doses of 0, 6, 24 and 48 g kg-1 of biomass ash (BA) to four different soils to reduce potential negative effects of tetracycline antibiotics. Specifically, soil samples were polluted with different concentrations of tetracycline, oxytetracycline or chlortetracycline, and the bacterial community growth was estimated using the 3H leucine incorporation technique. Soil amendment with BA increased soil pH (1.3-4.8 units), total carbon (0.7-5.8 g kg-1) and Fe and Al oxides concentrations (0.25-3.98 g kg-1), as well as bacterial activity (1-9 times compared to the control). In addition, BA amendment at high doses (24 or 48 g kg-1) resulted in a similar toxicity decrease for the three antibiotics, but with variations among soils. The reductions in antibiotics toxicity were very variable, ranging between 5% and 100% (total recovery). In view of that, the spreading of BA could be interesting as management practice to reduce risks of soil pollution and subsequent toxicity on bacterial communities due to tetracycline antibiotics.

Litterfall Hg deposition to an oak forest soil from southwestern Europe.

Litterfall constitutes one of the main vectors for mercury (Hg) transfer to forested ecosystems, so we studied the deposition of Hg through senescent vegetation (oak leaves, twigs and miscellaneous) in a deciduous forest plot of Southwest Europe dominated by Quercus robur in 2015 and 2016. Total Hg concentrations increased in the following order: bole wood (1.4 µg kg-1) < bark (8.3 µg kg-1) < twigs (12.2 µg kg-1) < miscellaneous (36.0 µg kg-1) < oak leaves (39.3 µg kg-1) < mineral soil (42.4 µg kg-1) < Oi horizons (48.7 µg kg-1) < Oe + Oa horizons (71.6 µg kg-1). Mercury accumulation rates in oak leaves during the growing season were 0.15-0.18 µg kg-1 day-1. Mercury deposition fluxes were 26 and 21 µg m-2 yr-1 for 2015 and 2016, respectively, with oak leaves being the fraction that contributed the most. Mercury determination in litterfall sorted biomass fractions lead to a more accurate estimation of the total annual Hg deposition fluxes through litterfall. Higher Hg content was obtained for organic horizons (average of 60.2 µg kg-1) than for mineral soil (mean of 42.4 µg kg-1), but the soil Hg pool was higher in the latter. The results confirmed the necessity of taking into account the Hg pool in the deeper mineral soil layers as they accumulate substantial quantities of Hg associated to organic C and Al compounds, preventing its mobilization to other compartments of the terrestrial ecosystems.

Adsorption-desorption of doxycycline in agricultural soils: Batch and stirred-flow-chamber experiments.

With the aim of obtaining information about the environmental fate and dynamics of the antibiotic doxycycline (DC) when it reaches soil, adsorption and desorption processes were studied for this compound in 20 agricultural soils, by means of batch-type and stirred-flow-chamber experiments. The results indicate that the studied soils adsorbed high amounts of DC, with adsorption percentages >91% in all cases. In addition, adsorption results were satisfactorily modeled, with good fittings to the Langmuir and Freundlich equations, with the values for Langmuir's maximum adsorption capacity (qmax) varying between 14,692 and 26,141 µmol kg-1 (average 17,816), and between 1,906 and 13,120 Ln µmol1-n kg-1 (average 6,969) for the Freundlich affinity coefficient, which are very high. The soil variables most related to the adsorption of the antibiotic were linked to organic matter (specifically, soil organic carbon-SOC- and soil nitrogen -N- contents), and to the clay fraction, as well as to cation exchange capacity, being the soils with a greater content in these variables those that presented a greater adsorption. FTIR results shown that DC adsorption mechanisms were based on interactions such as hydrogen bonds and π-π interactions between the antibiotic and soils. Desorption was very low, reaching values between 1 and 2% in batch experiments, and between 5 and 15% in stirred flow chamber experiments, which indicates a strong hysteresis affecting adsorption and desorption processes. This fact can be considered positively, as these soils could retain DC very strongly, thus reducing risks to human and ecological health.

Estimation of adsorption/desorption Freundlich's affinity coefficients for oxytetracycline and chlortetracycline from soil properties: Experimental data and pedotransfer functions.

Tetracycline antibiotics spread in the environment constitute a real threat, causing risks that should be controlled. Retention/release of these compounds after interacting with soil components are the main process governing their entry into water bodies, plant uptake, and availability for soil microorganisms. In this work, batch-type experiments were performed to study adsorption/desorption of oxytetracycline (OTC) and chlortetracycline (CTC) in 63 crop soils. The Freundlich model satisfactory described adsorption curves, showing strong affinity of both antibiotics to soils, with adsorption coefficient (KF(ads)) values between 1015 and 9733 Ln µmol1-n kg-1 for OTC, and between 1099 and 11344 Ln µmol1-n kg-1 for CTC. Desorption percentages were always lower than 10%, indicating that adsorption is highly irreversible. Furthermore, the desorption coefficient (KF(des)) correlated positive and significantly with KF(ads), showing that those soils characterized by higher adsorption were also those showing less desorption. Soil organic carbon (SOC) was the soil characteristic that most explained the variance of KF, both for adsorption and desorption, which caused that soils with higher SOC scores showed higher adsorption and lower desorption for both antibiotics. Pedotransfer functions were developed for OTC and CTC, and resulted effective to satisfactory predict KF(ads) and KF(des) values. These equations would facilitate an easy identification of soils vulnerable to antibiotics pollution, which would allow to program appropriate management practices to decrease undesirable effects on the environment and on public health.

Influence of mussel shell, oak ash and pine bark on the adsorption and desorption of sulfonamides in agricultural soils.

Taking into account the high mobility and environmental risks due to sulfonamide antibiotics as emerging pollutants, batch-type experiments were performed to study adsorption/desorption of three sulfonamides (sulfadiazine -SDZ-, sulfamethazine -SMT- and sulfachloropyridazine -SCP-) in three agricultural soils. The study was carried out both for un-amended and amended soil samples, using different doses (0, 12, 24 and 48 Mg ha-1) of three different by-products (mussel shell, oak ash and pine bark). Adsorption on un-amended soils was rather low, with percentages between 11 and 45% for SDZ, 20-64% for SMT, and 19-65% for SCP. Both the Linear and Freundlich models fitted well to adsorption curves. In the case of un-amended soils, and regarding the Linear model, the values of the coefficient of distribution (Kd, expressed in L kg-1) were between 0.6 and 1.3 for SDZ, between 0.7 and 1.1 for SMT, and between 0.6 and 2.6 for SCP. As regards the Freundlich model, the values of the adsorption constant (KF, expressed in L1/n µmol1-1/n kg-1), were in the range 0.4-1.9 for SDZ, 0.9-2.9 for SMT, and 1.2-3.8 for SCP. Simultaneously, desorption percentages were high, reaching 13.7-47.7% for SDZ, 12.6-35.1% for SMT, and 13.7-34.3% for SCP, when the highest initial antibiotic concentration (50 µmol L-1) was added, thus indicating low retention and high mobility for these compounds in soils. Mussel shell and oak ash amendments did not increase retention of any of the three sulfonamides. However, the incorporation of pine bark resulted in an increase in the adsorption and decrease in desorption for all three antibiotics. Specifically, for soils amended with pine bark at 48 Mg ha-1, Kd values (expressed in L kg-1) were between 2.1 and 2.9 for SDZ, between 3.4 and 3.6 for SMT, and between 2.5 and 8.2 for SCP. Regarding KF (expressed in L1/n µmol1-1/n kg-1), its values ranged from 5.6 to 6.3 for SDZ, 6.2-8.8 for SMT, and 5.3-7.1 for SCP. These scores were clearly higher than those of un-amended soils, and pine bark amendment also resulted in lower desorption percentages, ranging 8.7-11.4% for SDZ, 4.0-10.7% for SMT, and 6.5-16.9% for SCP. This positive effect on the retention of sulfonamides due to pine bark can be attributed to its high organic carbon content (48.6%), as well as to its acidic pHw (4.0). Therefore, pine bark amendment can be considered an effective alternative to increase the retention of sulfonamides in soils, thus reducing their bioavailability and transport to other environmental compartments, and subsequent risks of negative impacts on human and environmental health.

Effects of pine bark amendment on the transport of sulfonamide antibiotics in soils.

In the present work, laboratory column experiments were carried out to study the effect of pine bark amendment (at doses of 0, 12, 48 and 96 Mg ha-1) on the transport of three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) through two crop soils. All three sulfonamides showed high mobility in the unamend soils, with absence of retention in most cases. However, some differences were detected regarding the degree of interactions between sulfonamides and soils, being higher for soil 1, which was attributed to its higher organic carbon content. For both soils, interactions with the antibiotics studied followed the sequence SDZ < SMT < SCP, indicating an increase as a function of the hydrophobicity of sulfonamides. Pine bark amendment significantly increased the retention of the three sulfonamides in both soils. Specifically, in the case of soil 1, the incorporation of the highest dose of pine bark (96 Mg ha-1) caused that retention increased from 0% to 70.3% for SDZ, from 2.7% to 71.3% for SMT, and from 0% to 85.4% for SCP. This effect of pine bark is mainly attributed to its high organic carbon content (48.6%), including substances with potential to interact and retain antibiotics, as well as to its acidic pH (4.5). Therefore, pine bark amendment would be an effective alternative to reduce the transport of sulfonamides in soils and, thus, decrease risks of passing to other environmental compartments, as well as harmful effects on the environment and public health.

Adsorption/desorption of sulfamethoxypyridazine and enrofloxacin in agricultural soils.

Adsorption and desorption processes were studied for the antibiotics sulfamethoxypyridazine (SMP) and enrofloxacin (ENR) in 20 agricultural soils devoted to wheat-potato and vine cultivation. Batch experiments were used to conduct kinetic studies, as well as to evaluate adsorption and desorption for different concentrations of antibiotics. The results indicated that adsorption curves were linear for SMP, while presented a certain curvature in the case of ENR. The adsorption of both antibiotics was fitted to a linear equation and to the Freundlich model. In the case of the linear equation, the values of the distribution coefficient Kd were lower for SMP (0.9-26.0 L kg-1) than for ENR (121-2345 L kg-1). In the Freundlich model, the values of the adsorption constant KF ranged between 1.7 and 34.0 Ln µmol1-n kg-1 for SMP, and between 829 and 3019 Ln µmol1-n kg-1 for ENR. A multiple regression analysis showed that, in the case of SMP, 78% of the variance of the adsorption parameter Kd was explained by soil organic carbon (SOC) and exchangeable magnesium (Mge) contents, while for ENR no significant relation was found. In addition, for SMP, 66% of the variance of KF was explained by SOC, and for ENR 45% of the variability of KF was explained by nitrogen content. Desorption rates were higher for SMP (reaching up to 24%) than for ENR (which reached up to 7%). Desorption percentages showed a potential relation with the adsorption parameter Kd for both SMP and ENR. These results could be useful to elucidate the evolution and dynamics of these emerging pollutants in soils and other environmental compartments, which could be of aid in controlling public health risks associated to them.

Adsorption/desorption and transport of sulfadiazine, sulfachloropyridazine, and sulfamethazine, in acid agricultural soils.

Batch-type experiments were used to study adsorption-desorption of three sulfonamides: sulfadiazine (SDZ) sulfachloropyridazine (SCP), and sulfamethazine (SMT), in five crop soils, whereas laboratory soil column experiments were employed to obtain data on transport processes. Adsorption results were satisfactorily adjusted to Linear and Feundlich equations, with R2 values above 0.95. Adsorption followed the sequence SDZ < SMT < SCP, showing higher values for soils with higher levels of organic carbon (OC) content. Conversely, desorption was higher in soils with less OC, and lower in soils with higher OC contents. The temporal moment analysis method gave values for the transport parameters τ and R which were significantly correlated with soil parameters related to organic matter, specifically OC and N concentrations. The higher retention of the three sulfonamides in soils with high organic matter content is a relevant fact, with value when programming management practices in agricultural soils, and specifically in relation to the spreading of animal manures, slurries, or waste containing these emerging pollutants.

Experimental data and model prediction of tetracycline adsorption and desorption in agricultural soils.

In this work, tetracycline (TC) adsorption and desorption were studied, and the soil properties that most influenced the process were identified. Batch experiments were carried out on 63 crop soil samples, which showed a wide range of values in their physicochemical characteristics. Adsorption curves fit well to the Freundlich equation, with KF values varying between 901 and 9202 Ln µmol1-n kg-1. Kd values ranged between 53 and 6899 L kg-1 for an initial concentration (Co) of 400 µM, whereas the adsorption capacity (qa) ranged from 8541 to 14,852 µmol kg-1. TC retention on soils was high, with adsorption values always higher than 58%, and desorption values lower than 9%. Bivariate correlations and multiple linear regressions were performed to identify those soil variables having a greater influence on TC adsorption and desorption. The results indicate that organic carbon, clay, exchangeable aluminum, available phosphorus, effective cation exchange capacity content, and pH are the main characteristics affecting TC adsorption and desorption. The models, developed by means of multiple linear regression, gave satisfactory and robust predictions for TC adsorption and desorption, using easily determinable soil characteristics as input.

Pedotransfer functions to estimate the adsorption and desorption of sulfadiazine in agricultural soils.

Batch-type experiments were used to study adsorption-desorption of sulfadiazine in 50 crop soils exposed to antibiotic pollution due to the spreading of animal manure or slurry. Adsorption and desorption curves were linear, and were satisfactorily described using the linear and Freundlich equations. The Freundlich adsorption constant (KF(ad)) showed low values (between 0.4 and 9.0 L1/n µmol1-1/n kg-1), which were similar to those of the adsorption constant for the linear model (Kd(ad), between 0.3 and 12.0 L kg-1). Furthermore, the desorption constant for the linear model (Kd(des)) showed higher values than those of Kd(ad), ranging between 1.6 and 29.3 L kg-1, while the values of the Freundlich desorption constant (KF(des)) ranged from 0.10 to 36.8 L1/n µmol1-1/n kg-1. The percentages of adsorption were very variable, ranging from 10 to 87%. The soil characteristics that most influenced adsorption-desorption were those related to soil organic matter (organic carbon and nitrogen contents), as well as the effective cation exchange capacity, and pH. In addition, statistically robust pedotransfer functions were obtained, allowing prediction of adsorption-desorption behavior for sulfadiazine from readily determinable soil parameters, such as pH or organic carbon content.

Copper and zinc in rhizospheric soil of wild plants growing in long-term acid vineyard soils. Insights on availability and metal remediation.

Total and available Cu and Zn levels were assessed in plant biomass, as well as in two rhizosphere fractions (tightly adhering rhizosphere (TAR), and loosely adhering rhizosphere (LAR)), in wild plants species from vineyard soils. Both TAR and LAR fractions were enriched in total Cu and Zn (1.7 and 1.6 times, respectively), and in available Cu and Zn (2.2 and 19.5 times, respectively), with the former being significantly higher for TAR than for LAR fractions. Mean values for total Cu accumulation in root and aerial biomass of the studied wild plants were 84 and 66 mg kg-1, respectively, being 57 and 79 mg kg-1 for Zn. No correlations were found among metal contents in plant biomass and available Cu and Zn concentrations in the rhizosphere fractions. Translocation factor (TF) values for Zn (range 1.0-3.5) indicate preferential accumulation in the aerial biomass in all the studied wild plants. On the contrary, TF for Cu shows a greater variability, depending on plant species, and ranging from 0.2 to 5.9. Regarding bioaccumulation factor (BAF), ranges were 0.03-0.27 and 0.13-0.58, for Cu and Zn, respectively. Results suggest that D. sanguinalis, P. hieracioides, S. viridis, and T. barbata could be useful for Cu remediation in the studied soils, by means of phytostabilization processes.

Degradation of sulfadiazine, sulfachloropyridazine and sulfamethazine in aqueous media.

Antibiotics discharged to the environment constitute a main concern for which different treatment alternatives are being studied, some of them based on antibiotics removal or inactivation using by-products with adsorbent capacity, or which can act as catalyst for photo-degradation. But a preliminary step is to determine the general characteristics and magnitude of the degradation process effectively acting on antibiotics. A specific case is that of sulfonamides (SAs), one of the antibiotic groups most widely used in veterinary medicine, and which are considered the most mobile antibiotics, causing that they are frequently detected in both surface- and ground-waters, facilitating their entry in the food chain and causing public health hazards. In this work we investigated abiotic and biotic degradation of three sulfonamides (sulfadiazine -SDZ-, sulfachloropyridazine -SCP-, and sulfamethazine -SMT-) in aqueous media. The results indicated that, in filtered milliQ water and under simulated sunlight, the degradation sequence was: SCP > SDZ ≈ SMT. Furthermore, the rate of degradation clearly increased with the raise of pH: at pH 4.0, half-lives were 1.2, 70.5 and 84.4 h for SCP, SDZ and SMT, respectively, while at pH 7.2 they were 2.3, 9.4 and 13.2 h for SCP, SMT and SDZ. The addition of a culture medium hardly caused any change in degradation rates as compared to experiments performed in milliQ water at the same pH value (7.2), suggesting that in this case sulfonamides degradation rate was not affected by the presence of some chemical elements and compounds, such as sodium, chloride and phosphate. However, the addition of bacterial suspensions extracted from a soil and from poultry manure increased the rate of degradation of these antibiotics. This increase in degradation cannot be attributed to biodegradation, since there was no degradation in the dark during the time of the experiment (72 h). This indicates that photo-degradation constitutes the main removal mechanism for SAs in aqueous media, a mechanism that in this case was favored by humic acids supplied with the extracts from soil and manure. The overall results could contribute to the understanding of the environmental fate of the three sulfonamides studied, aiding to program actions that could favor their inactivation, which is especially relevant since its dissemination can involve serious environmental and public health risks.

Biotic and abiotic dissipation of tetracyclines using simulated sunlight and in the dark.

Veterinary antibiotics reaching soils and water bodies are considered emerging pollutants deserving special attention. In this work, dissipation of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) is investigated. Dissipation experiments in filtered water, using simulated sunlight, resulted in the following degradation sequence: TC < OTC ≈ CTC, with half-life values of 229, 101 and 104 min, respectively; however, no dissipation took place in the dark. Dissipation of the three tetracyclines in culture medium and with simulated sunlight was much higher, giving the sequence TC ≈ OTC < CTC, with half-lives of 9, 10 and 7 min, respectively; in the dark, TC and OTC did not suffer dissipation, but it was around 28% for CTC at the end of the experiment (480 min). The variable explaining a higher dissipation in culture medium and with light was pH, as this parameter caused changes in the distribution of species of tetracyclines, affecting degradation. Adding bacterial suspensions extracted from soil and poultry manure increased dissipation, giving the sequence: TC ≈ OTC < CTC, which is attributed to the presence of humic acids, which adsorb these antibiotics. These results could facilitate understanding the fate of antibiotics reaching environmental compartments and causing public health hazards.

Retention and transport of mecoprop on acid sandy-loam soils.

Interaction with soil components is one of the key processes governing the fate of agrochemicals in the environment. In this work, we studied the adsorption / desorption and transport of mecoprop (methylchlorophenoxypropionic acid or MCPP) in four acid sandy-loam soils with different organic matter contents. Kinetics of adsorption and adsorption/desorption at equilibrium were studied in batch experiments, whereas transport was studied in laboratory columns. Adsorption and desorption were found to be linear or nearly-linear. The kinetics of mecoprop adsorption were relatively fast in all cases (less than 24h). Adsorption and desorption were adequately described by the linear and Freundlich models, with KF values that ranged from 0.7 to 8.8Ln µmol1-nkg-1 and KD values from 0.3 to 3.6Lkg-1. The results of the transport experiments showed that the retention of mecoprop by soil was very low (less than 6.2%). The retention of mecoprop by the soils in all experiments increased with organic matter content. Overall, it was observed that mecoprop was weakly adsorbed by the soils, what would result in a high risk of leaching of this compound in the environment.

Removal of anionic pollutants by pine bark is influenced by the mechanism of retention.

The use of organic biosorbents for anion removal from water has been less studied than for cationic compounds. In this work, the removal capacity of pine bark for potential anionic pollutants (fluoride, phosphate, arsenate and dichromate) was assessed in column experiments, designed to study the process of transport. The results showed that pine bark has a very low retention capacity for phosphate, arsenate or fluoride, and in turn, very high for dichromate, with retention values close to 100% and less than 2% desorption of the adsorbed dichromate. The large differences observed between anions suggest that differences in the retention mechanism of each anion exist. In the case of phosphate and arsenate, electrostatic interactions with the mostly negatively charged functional groups of the pine bark determine the low retention capacity. Dichromate retention might proceed through reduction of chromium (VI) to chromium (III), what improves the efficiency of the removal.