Assessment of polluted soil remediation using bacterial community tolerance to heavy metals as an indicator

The assessment of remediation on metal-polluted soils is usually focused on total and/or bioavailable metal content. However, these chemical variables do not provide direct information about reductions in heavy metals pressure on soil microorganisms. We propose the use of bacterial communities to evaluate the efficiency of three remediation techniques: crushed mussel shell (CMS) and pine bark (PB) as soil amendments and EDTA-washing. A soil sample was polluted with different doses of Cu, Ni, and Zn (separately). After 30 days of incubation, the remediation techniques were applied, and bacterial community tolerance to heavy metals determined. If bacterial communities develop tolerance, it is an indicator that the metal is exerting toxicity on them. Soil bacterial communities developed tolerance to Cu, Ni, and Zn in response to metal additions. After remediation, bacterial communities showed decreases in bacterial community tolerance to Cu, Ni, and Zn for all remediation techniques. For Cu and Ni, soil EDTA-washing showed the greatest reduction of bacterial community tolerance to Cu and Ni, respectively, while for Zn the soil amendment with PB was the most effective remediation technique. Thus, bacterial community tolerance to heavy metals successfully detect differences in the effectiveness of the three remediation techniques.Ministerio de Economía y Competitividad | Ref. CTM2015-73422-JINMinisterio de Economía, Industria y Competitividad | Ref. RYC-2016-20411Región de Murcia | Ref. 21525/EE/21Xunta de Galicia | Ref. ED401A-2020/08

Dissolved organic matter as a confounding factor in the determination of pollution-induced community tolerance (PICT) of bacterial communities to heavy metals using the leucine incorporation method

PICT methodology using the leucine incorporation method (Leu-PICT) is useful for assessing heavy metal contamination in soils. First, bacterial community is exposed to metal in the soil (selection phase), developing tolerance if metal exerts toxicity. Secondly, in detection phase, bacterial suspensions are obtained, and tolerance is quantified by a second exposition of bacterial community to the metal using Leu-PICT methodology. However, during detection phase when Leu-PICT is performed, some characteristics of bacterial suspensions may change metal bioavailability. We assess the influence of dissolved organic matter (DOM) in bacterial suspensions, as humic acids (HA), on Leu-PICT determination to Cr, Cu, Ni, Pb and Zn. Results showed that the presence of HA in bacterial suspensions causes underestimations of bacterial community tolerance to Cr (increasing Cr toxicity), and overestimations of bacterial community tolerance to Cu, Ni, Pb, and Zn (reducing metal toxicity). In addition, the magnitude of these overestimations was different depending on the metal.Xunta de Galicia | Ref. ED401A-2020/084Ministerio de Economía y Competitividad | Ref. CTM2015-73422-JINFinanciado para publicación en acceso aberto: Universidade de Vigo/CISU

Soil abandonment as a trigger for changes in Zn fractionation in afforested former vineyard acidic soils

Zinc is an essential element for plant nutrition, but it may cause toxicity depending on its bioavailability and potential transformation in soil. In vineyard soils, high concentrations of Zn are usually found, mainly due to agricultural practices. However, a great abandonment of vineyards has recently occurred, leading to changes in the total and bioavailable Zn concentrations, as well as Zn fractionation. We analyzed Zn concentrations (total, ZnT, and bioavailable, ZnED) and fractionation in the soil of three paired sites (PM, PT, and AR) up to depths of 50 cm in active and adjacent abandoned vineyards that were already transformed into forests. The ZnT averaged at 210 mg kg−1 among all studied vineyards. The results showed changes in the vertical pattern ZnT concentrations after vineyard abandonment at the PM and PT sites, while at the AR site, no great variation occurred. The ZnED (mean values = 7 mg kg−1) decreased after abandonment at PM and AR in the uppermost surface layers, while it increased in the top 10 cm at the PT site, reaching up to 60 mg kg−1. Regarding Zn fractionation in active vineyards, the residual fraction (ZnR) was the most abundant, followed by Zn bound to crystalline Fe and Al oxy-hydroxides (ZnC) and Zn bound to soil organic matter (ZnOM). After abandonment, the ZnR slightly increased and the ZnC slightly decreased at the PM and AR sites at all depths, while the ZnOM showed a noticeable variation in the uppermost 10 cm of the PT site. These results suggest that the soil organic matter that is provided during afforestation may play an important role in Zn fractionation and mobilization, depending on its humification degree and chemical stability. Zn mobilization could result in a positive nutrient supply for plants, but caution must be taken, since an excess of Zn could cause toxicity in long-term abandoned vineyards.Xunta de Galicia | Ref. ED431C2021/46-GRCAgencia Estatal de Investigación | Ref. JC2020-044426-IUniversidade de Vig

Copper accumulation and fractionation in vineyard soils from temperate humid zone (NW Iberian Peninsula)

The occurrence of total Cu and Cu fractions (exchangeable Cu, Cu bound to organic matter, Cu bound to amorphous inorganic materials, Cu bound to crystalline Fe and Al oxides and residual Cu) was studied in 170 surface layers of soils from seven vineyard regions located in the NW Iberian Peninsula (Rías Baixas, Ribeira Sacra, Ribeiro, Monterrei, Valdeorras, O Bierzo and Vinhos Verdes). The data showed that long-term application of Cu-based fungicides has led to increased concentrations, mainly in superficial vineyard soil layers. Thus, 64% of the samples showed total Cu levels higher than 100 mg kg 1, threshold for soil contamination. Total Cu content in Ribeiro (248 ± 130 mg kg 1) and Ribeira Sacra (259 ± 118 mg kg 1) soils were significantly higher than those observed for the rest of the vineyard regions (169 ± 90, 139 ± 122, 115 ± 42, 103 ± 42 and 100 ± 48 mg kg 1 in Valdeorras, Rías Baixas, O Bierzo, Vinhos Verdes and Monterrei, respectively). Cu distribution among various soil fractions also differed between winegrowing regions; however, in general, Cu in these vineyard soils is present mainly in less mobile fractions (average values were 48 ± 12% for Cu bound to soil organic matter; 15 ± 9% for Cu associated to amorphous inorganic materials; 12 ± 9% for Cu bound to crystalline Fe and Al oxides and 23 ± 12% for residual Cu), whereas exchangeable Cu constituted approximately 3 ± 3% of total Cu. All soil samples were separated in three well differentiated groups according to their physical, chemical and Cu fractionation data (Ribeiro, Ribeira Sacra and Monterrei samples; O Bierzo, Valdeorras and Monterrei samples; Rías Baixas and Vinhos Verdes samples), being soil type, climate and fungicide application as the most determinant factors for soil quality.Xunta de Galici

Microbial community structure of vineyard soils with different pH and copper content

The phospholipid fatty acid (PLFA) pattern of vineyard soils from the Northwest of the Iberian Peninsula was studied to identify soil factors determining the microbial community structure, with special emphasis on effects of Cu pollution and pH. A wide range of soil samples, collected from six winegrowing regions (Rías Baixas, Ribeiro, Ribeira Sacra, Monterrei, Valdeorras and Vinhos Verdes) was analyzed. Physico-chemical properties, including total Cu content, five different Cu fractions and available Cu, were also determined. Total Cu varied between 33 and 1120 mg kg1 and pHwater between 4.3 and 7.3. Soil pH rather than Cu content was most important in determining the composition of the microbial community. An increase in the relative concentrations of the monounsaturated PLFAs 16:1ω5, 16:1ω7c, 17:1ω8 and 18:1ω7 and a decrease of br18:0, i17:0, 17:0 and cy19:0 was correlated to an increase in pH. A significant effect of Cu was also found, with an increase in the branched fatty acids 10Me17:0, i16:0, 10Me18:0, a17:0 and br17:0 as consequence of Cu pollution. This change in the PLFA pattern was correlated to both the total and available fractions of Cu. Although the PLFA pattern was a useful tool to assess factors affecting the microbial composition, it is difficult to differentiate between these factors.Xunta de Galicia | Ref. 09MDS013291P

Estimation of baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn in unpolluted soils, a background for PICT (pollution-induced community tolerance) determination

The PICT method (pollution-induced community tolerance) can be used to assess whether changes in soil microbial response are due to heavy metal toxicity or not. Microbial community tolerance baseline levels can, however, also change due to variations in soil physicochemical properties. Thirty soil samples (0–20 cm), with geochemical baseline concentrations (GBCs) of heavy metals and from five different parent materials (granite, limestone, schist, amphibolite, and serpentine), were used to estimate baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn using the leucine incorporation method. General equations (n = 30) were determined by multiple linear regression using general soil properties and parent material as binary variables, explaining 38% of the variance in log IC50 (concentration that inhibits 50% of bacterial growth) values for Zn, with 36% for Pb, 44% for Cr, and 68% for Ni. The use of individual equations for each parent material increased the explained variance for all heavy metals, but the presence of a low number of samples (n = 6) lead to low robustness. Generally, clay content and dissolved organic C (DOC) were the main variables explaining bacterial community tolerance for the tested heavy metals. Our results suggest that these equations may permit applying the PICT method with Zn and Pb when there are no reference soils, while more data are needed before using this concept for Ni and Cr.This study has been funded by the Spanish Ministry of Economy and Competitiveness through the project CTM2015-73422-JIN (FEDER Funds). David Fernández-Calviño holds a Ramón y Cajal contract (RYC-2016–20411) fnanced by the Spanish Ministry of Economy, Industry and Competitiveness. Claudia CampilloCora holds a predoctoral fellowship fnanced by Xunta de Galicia (ED481A-2020/084). Diego Soto-Gómez was supported by a postdoctoral fellowship from the Spanish Ministry of Education “Juan de la Cierva Formación (FJC2019-039176-I).

SARS-CoV-2 and other main pathogenic microorganisms in the environment: situation in Galicia and Spain

In the context of the current COVID-19 pandemic, and mostly taking a broad perspective, it is clearly relevant to study environmental factors that could affect eventual future outbreaks due to coronaviruses and/or other pathogenic microorganisms. In view of that, the authors of this manuscript review the situation of SARS-CoV-2 and other main pathogenic microorganisms in the environment, focusing on Galicia and Spain. Overall, in addition to showing local data, it is put in evidence that, summed to all efforts being carried out to treat/control this and any other eventual future epidemic diseases, both at local and global levels, a deep attention should be paid to ecological/environmental aspects that have effects on the planet, its ecosystems and their relations/associations with the probability of spreading of eventual future pandemicsThis work was supported by the Spanish Ministry of science, innovation and universities [grant numbers RTI2018-099574-B-C21 and RTI2018-099574-B-C22]. It also received funds from the European Regional Development Fund (ERDF) (FEDER in Spain), being a complement to the previous grants, without additional grant numberS

Changes in Cu accumulation and fractionation along soil depth in acid soils of vineyards and abandoned vineyards (now forests)

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThis study investigated changes in copper accumulation and fractionation based on the depth of soils obtained from active and abandoned vineyards. Soil samples were collected at different depths in three areas with active and abandoned vineyards, and the concentrations of total copper and copper fractions were measured in these soil samples. Results revealed that in active vineyards, total copper accumulation was the highest in the first layer of soil (depth = 0–2 cm), with concentrations (193–892 mg kg−1) considerably higher than those in the deepest soil layer (depth = 40–50 cm; concentration = 63–71 mg kg−1). This accumulation was significantly correlated with the total carbon concentration in the soil. However, the total copper concentration in abandoned vineyards (84–374 mg kg−1) was the highest in the subsurface layers (depth = 10–15 cm) and was not significantly correlated with the total carbon content. Moreover, the percentage of available copper was lower in abandoned vineyards than in active vineyards. In terms of copper fractionation, the main fraction in active vineyard soil was copper bound to organic matter, whereas the main fraction in abandoned vineyard soil was residual copper. Therefore, vineyard abandonment and its transformation into forest changed the distribution and fractionation of copper based on soil depth, thus decreasing the amount of available copper and improving the soil quality, which could enable new ecosystems.Xunta de Galicia | Ref. ED431F 2018/06Ministerio de Economía | Ref. RYC-2016–20411Xunta de Galicia | Ref. ED481D-2021/01

Copper content of soils and river sediments in a winegrowing area, and its distribution among soil or sediment components

This paper concerns copper levels in the components of soils and river sediments in a river basin partially devoted to vineyards that are regularly treated with copper-bearing grapevine fungicides. Copper concentrations were determined in 26 soil samples, 20 river sediment samples and 71 river water samples taken in a small basin with steep slopes suffering significant erosion. Mean total Cu concentration was 31 mg kg 1 in woodland soils, 30 mg kg 1 in pasture soils, and eight times higher, 246 mg kg 1 (range 157434 mg kg 1), in productive vineyard soils. Total copper concentration in river sediments ranged from 18 to 209 mg kg 1 depending on the proportion of land under vineyard in the sub-basin drained via the sampling point (r = 0.915, p < 0.05). Soils differed relatively little as regards the distribution of Cu among various fractions; in particular, about 50% of total copper content was generally bound to soil organic matter. The distribution of Cu in sediments was more heterogeneous: sandy sediments had copper distributions similar to those observed in soils, but in silty sediments with large inorganic colloids fractions it was these amorphous colloids that bound the largest proportion of copper (mean 31.5%). The absence of significant differences among water-soluble Cu concentrations at the various water-sampling points suggests that winegrowing does not increase water-soluble Cu levels in the river under normal circumstance