María Julieta Salazar

Effects of heavy metal concentrations (Cd, Zn and Pb) in agricultural soils near different emission sources on quality, accumulation and food safety in soybean [Glycine max (L.) Merrill]

Argentina is one of the major producers of soybean in the world, this generates a high global demand for this crop leading to find it everywhere, even close to human activities involving pollutant emissions. This study evaluated heavy metal content, the transfer of metals and its relation to crop quality, and the toxicological risk of seed consumption, through soil and soybean sampling. The results show that concentrations of Pb and Cd in soils and soybeans at several sites were above the maximum permissible levels. The heavy metal bioaccumulation depending on the rhizosphere soil compartment showed significant and high regression coefficients. In addition, the similar behavior of Cd and Zn accumulation by plants reinforces the theory of other studies indicating that these metals are incorporated into the plant for a common system of transport. On the other hand, the seed quality parameters did not show a clear pattern of response to metal bioacumulation. Taken together, our results show that soybeans grown nearby to anthropic emission sources might represent a toxicological hazard for human consumption in a potential Chinese consumer. Hence, further studies should be carried out taking into account the potential negative health effects from the consumption of soybeans (direct or indirect through consumption of meat from cattle) in these conditions.

Assessment of the root system of Brassica juncea (L.) czern. and Bidens pilosa L. exposed to lead polluted soils using rhizobox systems

ABSTRACT The purpose of this study was to compare the behavior of the root system of one of the most frequently cited species in phytoremediation Indian mustard [Brassica juncea (L.) Czern.] and a representative perennial herb (Bidens pilosa L.) native of Argentina, for different concentrations of lead in soils through chemical and visualization techniques of the rhizosphere. Lead polluted soils from the vicinity of a lead recycling plant in the locality of Bouwer, were used in juxtaposed rhizobox systems planted with seedlings of B. juncea and B. pilosa with homogeneous and heterogeneous soil treatments. Root development, pH changes in the rhizosphere, dry weight biomass, lead content of root and aerial parts and potential extraction of lead by rhizosphere exudates were determined. In both species lead was mainly accumulated in roots. However, although B. juncea accumulated more lead than B. pilosa at elevated concentrations in soils, the latter achieved greater root and aerial development. No changes in the pH of the rhizosphere associated to lead were observed, despite different extractive potentials of lead in the exudates of the species analyzed. Our results indicated that Indian mustard did not behave as a hyperaccumulator in the conditions of the present study.

Auxin effects on Pb phytoextraction from polluted soils by Tegetes minuta L. and Bidens pilosa L.: Extractive power of their root exudates.

The principal impediment for Pb uptake by plants is the Casparian strip in roots. It prevents metals reaching the xylem, thereby hampering translocation to the aerial organs. In the root apices, young root cells have thin cell walls and the Casparian strip is not completely developed, which could facilitate Pb uptake by roots at these vulnerable points. However, as the phytotoxic effects of Pb reduce root growth and enhance suberization, entry of Pb into the plant is avoided. We propose that the application of root growth promotors could be an important complement in the phytoextraction of Pb from polluted soils, due to their effects on produced biomass, Pb toxicity, and root exudate production. A greenhouse experiment was carried on to evaluate the auxin application effect on the Pb uptake of Bidens pilosa and Tagetes minuta. These species were sensitive to auxins, but the phytotoxic effect of Pb was not reversed by this treatment. Root exudates capable of extracting Pb were produced only when the species were grown in highly polluted soils, indicating a behavioral response to Pb exposure which is desirable for phytoremediation.

Accumulation of lead and associated metals (Cu and Zn) at different growth stages of soybean crops in lead-contaminated soils: food security and crop quality implications

Abstract The Pb, Cu and Zn content, the physicochemical parameters in soils (EC, OM%, soil texture and pH) and the metal accumulation of Glycine max plants at different growth stages were evaluated. Topsoil and soybean samples were collected in the vicinity of a former battery-recycling plant, with the results showing that only the concentrations of Pb in soils corresponding to sites located near to the lead emission source were above the maximum permissible levels. However, soybean crops accumulated Pb above the permitted levels at all studied sites, revealing a potential toxicological risk for direct consumption. Thus, the accumulation of Pb in soybean was directly related to the translocation factor of the metal from roots to aerial parts of the plant. This was evidenced as a lower accumulation at early growth stages and a higher accumulation at maturity, with the distribution between organs coinciding with nutrient incorporation and remobilization in the plant. Moreover, the bioconcentration factor revealed that the bioaccumulation of lead in soybean was a consequence of the lead-recycling plant activity in the past. Taken together, results of the present study demonstrated that soybean crops can incorporate and accumulate potentially toxic metals, such as lead.

Effects of co-cropping Bidens pilosa (L.) and Tagetes minuta (L.) on bioaccumulation of Pb in Lactuca sativa (L.) growing in polluted agricultural soils.

ABSTRACT Polluted agricultural soils are a serious problem for food safety, with phytoremediation being the most favorable alternative from the environmental perspective. However, this methodology is generally time-consuming and requires the cessation of agriculture. Therefore, the purpose of this study was to evaluate two potential phytoextractor plants (the native species Bidens pilosa and Tagetes minuta) co-cropped with lettuce growing on agricultural lead-polluted soils. The concentrations of Pb, as well as of other metals, were investigated in the phytoextractors, crop species, and in soils, with the potential risk to the health of consumers being estimated. The soil parameters pH, EC, organic matter percentage and bioavailable lead showed a direct relationship with the accumulation of Pb in roots. In addition, the concentration of Pb in roots of native species was closely related to Fe (B. pilosa, r = 0.81; T. minuta r = 0.75), Cu (T. minuta, r = 0.93), Mn (B. pilosa, r = 0.89) and Zn (B. pilosa, r = 0.91; T. minuta, r = 0.91). Our results indicate that the interaction between rhizospheres increased the phytoextraction of lead, which was accompanied by an increase in the biomass of the phytoextractor species. However, the consumption of lettuce still revealed a toxicological risk from Pb in all treatments.

Tagetes minuta L. Variability in Terms of Lead Phytoextraction from Polluted Soils: Is Historical Exposure a Determining Factor?

AbstractTagetes minuta L. is a plant which accumulates Pb under certain conditions, making it a candidate for phytoextraction projects because it also produces marketable essential oils without detectable Pb levels. Although extraction efficiency has been shown to significantly vary between individuals, these results have been obtained using only historically exposed populations, which leads to the questions: Is the ability to tolerate and accumulate Pb a property of the species? Or is it a characteristic of some individuals from a historically exposed population? In this context, a greenhouse experiment was performed to analyse the intrapopulation and interpopulation variability in response to Pb among individuals from historically unexposed and exposed populations. In addition, we also attempted to identify relationships between certain capabilities (toleration and accumulation of Pb) and the physiological parameters related to oxidative stress or the volatile compounds of the essential oils. The Pb concentration was determined by total reflection X-ray fluorescence, physiological parameters were obtained by spectrophotometry, and essential oils were analysed by gas chromatography. The results demonstrated that adequate tolerance and accumulation capabilities are present in T. minuta, irrespective of the exposure history. These findings may be associated to a hormesis response, which includes enhancement of pigments, biomass production and the uptake of other heavy metals such as micronutrients. Nevertheless, the historically exposed population had a better tolerance to Pb, since it presented defence characteristics reflected in the essential oil composition and in the avoidance of damage at the lipid peroxidation level after Pb uptake. Graphical abstractᅟ