Do heavy metals affect bacterial communities more in small repeated applications or in a single large application?

Heavy metals from anthropogenic sources accumulate slowly but steadily, leading to high metal concentration levels in soil. However, the effect of each heavy metal on soil bacterial communities is usually assessed in laboratories by a single application of individually spiked metals. We evaluated the differences between single individual application and repeated individual applications of Cr, Cu, Ni, Pb, and Zn on bacterial communities, through pollution-induced community tolerance (PICT), using bacterial growth as the endpoint (3H-leucine incorporation method). We found that PICT development was higher when soil was spiked in individual single application than individual repeated applications for Cu, Ni and Zn. In contrast, bacterial communities did not show different tolerance between singly or repeatedly when soil was spiked with Cr. In the case of Pb any increase of bacterial community tolerance to this metal was found despite high doses applied (up to 2000 mg kg-1). These results are relevant for the interpretation of the effects of heavy metals on soil microbes in order to avoid laboratory overestimations of the real effects of heavy metals on soil microbes.

Influence of soil properties on the development of bacterial community tolerance to Cu, Ni, Pb and Zn.

Pollution-Induced Community Tolerance (PICT) is a helpful and sensitive methodology to evaluate the effect of metal pollution in soils using microorganisms as indicators. PICT was used to determine the increase of bacterial community tolerance to Cu, Ni, Pb and Zn (Δlog IC50), and to assess the influence of soil properties on the development of bacterial community tolerance to Cu, Ni, Pb, and Zn. Soil samples showed a wide range of properties, such as pH (3.96-7.47), texture (13.8-31.7% clay) or organic matter (9.7-30.7%). Bacterial growth measured by the [3H]-leucine incorporation method was used as the PICT endpoint. Bacterial communities generally developed tolerance in response to Cu, Ni and Zn additions to soils. However, bacterial communities showed no tolerance to Pb, probably due to high Pb sorption in studied soils. Soil properties influenced the development of bacterial community tolerance to Cu, Ni and Zn. Effective cation exchange and a soil sorption parameter (Freundlich's linearity index) were the selected variables to estimate Δlog IC50 to Cu (R2 = 0.65). Clay content and Ni-soluble are the main factors to estimate Δlog IC50 to Ni (R2 = 0.63). Organic matter content and a sorption parameter (maximum sorption capacity of the soil from Langmuir equation) are the soil properties to estimate Δlog IC50 to Zn (R2 = 0.45). Most of the variables exerted their effect in soil, i.e. PICT selection phase. However, clay content affected bacterial community tolerance determination (PICT detection phase), leading to overestimated measurements of bacterial community tolerance.

Cu and As(V) Adsorption and Desorption on/from Different Soils and Bio-Adsorbents.

This research is concerned with the adsorption and desorption of Cu and As(V) on/from different soils and by-products. Both contaminants may reach soils by the spreading of manure/slurries, wastewater, sewage sludge, or pesticides, and also due to pollution caused by mining and industrial activities. Different crop soils were sampled in A Limia (AL) and Sarria (S) (Galicia, NW Spain). Three low-cost by-products were selected to evaluate their bio-adsorbent potential: pine bark, oak ash, and mussel shell. The adsorption/desorption studies were carried out by means of batch-type experiments, adding increasing and individual concentrations of Cu and As(V). The fit of the adsorption data to the Langmuir, Freundlich, and Temkin models was assessed, with good results in some cases, but with high estimation errors in others. Cu retention was higher in soils with high organic matter and/or pH, reaching almost 100%, while the desorption was less than 15%. The As(V) adsorption percentage clearly decreased for higher As doses, especially in S soils, from 60−100% to 10−40%. The As(V) desorption was closely related to soil acidity, being higher for soils with higher pH values (S soils), in which up to 66% of the As(V) previously adsorbed can be desorbed. The three by-products showed high Cu adsorption, especially oak ash, which adsorbed all the Cu added in a rather irreversible manner. Oak ash also adsorbed a high amount of As(V) (>80%) in a rather non-reversible way, while mussel shell adsorbed between 7 and 33% of the added As(V), and pine bark adsorbed less than 12%, with both by-products reaching 35% desorption. Based on the adsorption and desorption data, oak ash performed as an excellent adsorbent for both Cu and As(V), a fact favored by its high pH and the presence of non-crystalline minerals and different oxides and carbonates. Overall, the results of this research can be relevant when designing strategies to prevent Cu and As(V) pollution affecting soils, waterbodies, and plants, and therefore have repercussions on public health and the environment.

Retention of propiconazole and terbutryn on acid sandy-loam soils with different organic matter and Cu concentrations.

Equilibrium propiconazole and terbutryn adsorption characteristics were evaluated in ten acid vineyard soils with a wide range of organic matter and copper concentrations using batch experiments. Adsorption data from equilibrium adsorption experiments were generally well described by linear and Freundlich models. Parameters from these models showed that soil organic matter played a key role of propiconazole adsorption processes, but also the amorphous Fe oxides content in soils. Soil organic matter positively influenced terbutryn adsorption, whereas increases in exchangeable copper decreased terbutryn adsorption. Desorption experiments showed that both, propiconazole and terbutryn adsorption in soils was quite irreversible, i.e. the amount of pesticides desorbed after its adsorption was always less than 50%.

Use of participative methodology in oral health education for adolescents / Utilização de metodologia participativa na educação em saúde bucal para adolescentes

Objective: This paper describes a model of participative methodology used in the oral health education for teenagers. Methods: 16 teenagers aged between 10 and 14 years old participated. Focus groups were used to evaluate the topics of interest. The methodology evaluation was performed by the analysis of the material developed by the teenagers and an objective questionnaire, applied after the project completion. Results: By means of the focus group it was identified the following issues: problems due to bad breath in their relationships and the relationshipbetween lack of access to employment and precarious oral health. Ten meetings were held to discuss these issues and evaluate their relationshipwith oral health basics. The participation of adolescents was encouraged via movies and music available on the Internet. At the end of the meetings the group produced some educational materials and a comic book, which was analyzed and considered as a category 3: very rich design in content, objective concepts and clear goals. The questionnaire revealed that the right answers concentrated on the subjects which they have developed educational materials, such as self-care. 88% of the teenagers evaluated the project as very important, and an influencing factor in their improvement of oral health care. Conclusion: The use of a participative methodology for oral health education can, in fact, positively impact on changing teenagers behaviors. Third sector institutions that perform a well-planned and committed work can contribute to the promotion of oral health in Brazil.

Objetivo: Descrever um modelo de metodologia participativa utilizado na educação em saúde bucal de adolescentes. Métodos: Participaram 16 adolescentes com idades entre 10 e 14 anos. Para o conhecimento de temas de interesse foi utilizado o grupo focal. A avaliação da metodologia empregada foi realizada através da análise do material desenvolvido pelos adolescentes e de um questionário objetivo, aplicado após o término do projeto. Resultados: Através do grupo focal foi possível identificar os seguintes temas: problemas trazidos pelo mau-hálito em uma relação afetiva e a relação entre dificuldade de acesso ao emprego e recariedade da saúde bucal. Foram realizados 10 encontros para a discussão e relacionamento desses temas com conceitos básicos de saúde bucal. A participação dos adolescentes foi incentivada através de filmes disponíveis na Internet e músicas. Ao final dos encontros o grupo produziu alguns materiais educativos e um gibi, que foi analisado e considerado como categoria 3: desenho muito rico em conteúdo; conceitos objetivos e claros. O questionário demonstrou que as respostas certas se concentraram nos temas para os quais eles desenvolveram material didático,como o auto-cuidado. O projeto foi avaliado por 88% dos adolescentes como muito importante e como um fator que os influenciou na melhora do cuidado com a saúde bucal. Conclusão: A utilização de uma metodologia participativa de educação em saúde bucal pode, de fato, impactar positivamente na mudança de atitude dos adolescentes. Instituições do terceiro setor que realizem um trabalho comprometido e bem planejado podem contribuir para a promoção de saúde bucal no Brasil.