Enrique Navarro

Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi

Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidated.

Effects of atrazine on periphyton under grazing pressure.

An experiment was carried out using indoor experimental channels to assess the long-term effect (18 days) of herbivores (Physella acuta, Gastropoda) on periphyton communities exposed to low levels of atrazine (14 microg l(-1)). We hypothesized that herbivorism modifies the response of periphyton to atrazine. Carbon incorporation, chlorophyll-a content, biovolume and algal taxonomic composition in the channels that contained atrazine were not significantly different from the control channels (not receiving atrazine). In channels with grazers and atrazine, there was a significant reduction of carbon incorporation and algal density. In this treatment, physiognomic forms and algal composition were significantly different from the others. The biomass of grazers (measured as change in dry mass) was not significantly affected by the addition of atrazine. Grazers maintained low levels of periphyton biomass, enhancing algal cell exposition to toxicant and inhibiting any adaptation of the algae to the toxic exposure. The increase in atrazine toxicity with grazing not only affected the metabolism, but also the structure of the algal community, which suggests that effects were not transient but permanent.

Structure and function of benthic algal communities in an extremely acid river

The composition of algal species and pigments and the structural and functional characteristics of the algal community were investigated in an acid stream of southwestern Spain, the Río Tinto. The algal community had low diversity and showed few seasonal differences. It was mainly made up of Klebsormidium flaccidum Kütz. (Silva, Mattox & Blackwell) that produced long greenish or purplish filaments, Pinnularia acoricola Hust. (producing brown patches) and Euglena mutabilis Schmitz. The algal filaments made up a consistent biofilm that also included fungal hyphae, iron bacterial sheaths, diatoms, and mineral particles. HPLC analyses on Río Tinto samples showed that undegraded chl accounted for 67% of the total chl in the filamentous patches but were a minority in the brown patch (2.6%). The brown patch had a concentration of carotenoids eight times lower than that observed in the green patch. When chl concentrations were weighted for the proportion of the different patches on the streambed, undegraded chl a accounted for 89.2 mg chl a·m−2 of stream surface area (5.4 g C·m−2). This high algal biomass was supported by relatively high nutrient concentrations and by a high phosphatase activity (Vmax = 137.7 nmol methylumbelliferyl substrate·cm−2·h− 1 , Km = 0.0045 μM). The remarkable algal biomass in Río Tinto potentially contributed to the bacterial–fungal community and to the macroinvertebrate community and emphasizes the role that the algae may have in the organic matter cycling and energy flow in extreme systems dominated by heterotrophic microorganisms.

The effect of copper exposure on a simple aquatic food chain

The effect of copper (44 microg l(-1)) on a simple food chain was studied using indoor experimental channels to identify the changes in periphyton community (metabolism, chlorophyll a content, abundance, composition and lipid and protein content) and in herbivore (Stagnicola vulnerata) growth rate and reproduction. The algal community was sensitive to copper at the beginning but differences between treatments were not significant during the experiment. However, copper affected growth rate, reproduction and embryo hatching on snails. These results indicate that the effects on snails are more sensitive endpoints in assessing sublethal copper toxicity than effects on periphyton.

Use of microbenthic algal communities in ecotoxicological tests for the assessment of water quality: the Ter river case study

The tolerance of microbenthic algal communities to two model toxicants,atrazine and copper, was studied in the Ter river during spring and summer.Artificial substrata were colonised at 9 sites and used to perform short-term(1–4 h) toxicity tests in the laboratory and to obtain photon yield as theecotoxicological endpoint. The tolerance was lower in spring than insummer for both toxic substances and varied according to the site studied.Copper toxicity was associated with physico-chemical conditions (totalsuspended solids and water pH) and, especially, with severalbiomass-related parameters, whereas atrazine toxicity was related to algalabundance and species composition. Temporal and spatial changes innutrient concentration may alter the biomass and species composition ofthe communities and thus affect their tolerance to toxic substances. It hasto be therefore considered that the environmental characteristics of theriver system may determine relevant direct and indirect effects on the algalcommunities, then affecting their specific ecotoxicological responses. Oncethis is assumed, the empirical expressions obtained on calculatingEC50 and EC10 can be used to predict the community-leveltransient effects of toxic exposures.

Effects of copper on algal communities at different current velocities

This study examines the influence of current velocity in the toxiceffect of copper in diatom-dominated biofilms grown in artificial channels.Effects on community structure, algal biomass and photosynthesis (carbonincorporation) caused by 15 μg L−1 of copperwere tested at contrasting (1 and 15 cm s−1)velocities. Moreover, a possible threshold on the effect of copper on algalbiomass and photosynthesis related to current velocity was examined by usingprogressively increasing current velocity (1 to 50 cms−1) at 15 μg L−1 Cu.Chlorophyll-a decreased ca. 50% as a result of addition of15 μg L−1 Cu. Chlorophyll decrease occurredearlier at 15 cm s−1 than at 1 cms−1 when adding 15 μg L−1Cu. Copper also caused a remarkable decrease in carbon incorporation(from 30 to ca. 50%), which was produced earlier at 15 cms−1 (three days) than at 1 cms−1 (seven days). Some taxa were affected by thecombination of copper and current velocity. Both Achnanthesminutissima and Stigeoclonium tenue becomedominant at 15 cm s−1 in the presence of copper.Significant inhibition of algal growth in 15 μg L−1Cu occurred at low (1 cm s−1) and highvelocities (50 cm s−1), but not at intermediatevelocity (20 cm s−1). The experiments indicatethat current velocity triggers the effect that copper has on diatom-dominatedbiofilms, and that the effect is more remarkable at low and high than atintermediate current velocities.

Ecological classification of a set of Mediterranean reservoirs applying the EU Water Framework Directive: A reasonable compromise between science and management

Abstract The Water Framework Directive EU2000/60/EC (WFD) was implemented for reservoirs at a regional scale (northeastern Spain). Twenty-one reservoirs were monitored quarterly over the course of a year. Using principal component analysis, the reservoirs were classified into types according to their geological and morphometric features. The Ecological Quality (EQ) of the reservoirs was assessed by integrating values of total chlorophyll a, cyanophyta chlorophyll a concentration, fish metrics, Secchi depth, averaged hypolimnetic oxygen concentration and total phosphorus. For each reservoir type, a reference condition of quality was selected. When possible, this reference was the reservoir displaying the best EQ; otherwise expert judgment was used. To allow comparison of quality among reservoirs belonging to different types, thus identifying intrinsic differences, an Ecological Quality Ratio (EQR) was calculated by dividing the EQ value of each reservoir by that of its reference. According to EQR, the majority of the reservoirs accomplished the quality criteria of the WFD. This study identified a number of useful indicators for EQ assessment. Moreover, because the references were chosen among similar reservoirs, low EQR values are indicative of specific problems, such as untreated or wastewater spills or droughts. The results also demonstrate that expert judgment is a reasonable compromise when the low number of water bodies available for the study prevents statistical approaches.

Irrigation agriculture affects organic matter decomposition in semi-arid terrestrial and aquatic ecosystems

Many dryland areas are being converted into intensively managed irrigation crops, what can disrupt the hydrological regime, degrade soil and water quality, enhance siltation, erosion and bank instability, and affect biological communities. Still, the impacts of irrigation schemes on the functioning of terrestrial and aquatic ecosystems are poorly understood. Here we assess the effects of irrigation agriculture on breakdown of coarse organic matter in soil and water. We measured breakdown rates of alder and holm oak leaves, and of poplar sticks in terrestrial and aquatic sites following a gradient of increasing irrigation agriculture in a semi-arid Mediterranean basin transformed into irrigation agriculture in 50% of its surface. Spatial patterns of stick breakdown paralleled those of leaf breakdown. In soil, stick breakdown rates were extremely low in non-irrigated sites (0.0001-0.0003 day(-1)), and increased with the intensity of agriculture (0.0018-0.0044 day(-1)). In water, stick breakdown rates ranged from 0.0005 to 0.001 day(-1), and increased with the area of the basin subject to irrigation agriculture. Results showed that irrigation agriculture affects functioning of both terrestrial and aquatic ecosystems, accelerating decomposition of organic matter, especially in soil. These changes can have important consequences for global carbon budgets.

Analysis of the Diversity of Substrate Utilisation of Soil Bacteria Exposed to Cd and Earthworm Activity Using Generalised Additive Models

Biolog EcoPlates™ can be used to measure the carbon substrate utilisation patterns of microbial communities. This method results in a community-level physiological profile (CLPP), which yields a very large amount of data that may be difficult to interpret. In this work, we explore a combination of statistical techniques (particularly the use of generalised additive models [GAMs]) to improve the exploitation of CLPP data. The strength of GAMs lies in their ability to address highly non-linear relationships between the response and the set of explanatory variables. We studied the impact of earthworms (Aporrectodea caliginosa Savigny 1826) and cadmium (Cd) on the CLPP of soil bacteria. The results indicated that both Cd and earthworms modified the CLPP. GAMs were used to assess time-course changes in the diversity of substrate utilisation (DSU) using the Shannon-Wiener index. GAMs revealed significant differences for all treatments (compared to control -S-). The Cd exposed microbial community presented very high metabolic capacities on a few substrata, resulting in an initial acute decrease of DSU (i.e. intense utilization of a few carbon substrata). After 54 h, and over the next 43 h the increase of the DSU suggest that other taxa, less dominant, reached high numbers in the wells containing sources that are less suitable for the Cd-tolerant taxa. Earthworms were a much more determining factor in explaining time course changes in DSU than Cd. Accordingly, Ew and EwCd soils presented similar trends, regardless the presence of Cd. Moreover, both treatments presented similar number of bacteria and higher than Cd-treated soils. This experimental approach, based on the use of DSU and GAMs allowed for a global and statistically relevant interpretation of the changes in carbon source utilisation, highlighting the key role of earthworms on the protection of microbial communities against the Cd.

Impacts of agricultural irrigation on nearby freshwater ecosystems: the seasonal influence of triazine herbicides in benthic algal communities.

A small hydrological basin (Lerma, NE Spain), transformed from its natural state (steppe) to rain-fed agriculture and recently to irrigation agriculture, has been monitored across four seasons of an agricultural year. The goal of this study was to assess how and whether agricultural activities impacted the nearby freshwater ecosystems via runoff. Specifically, we assessed the toxicity of three triazine herbicides, terbuthylazine, atrazine and simazine on the photosynthetic efficiency and structure of algal benthic biofilms (i.e., phototropic periphyton) in the small creek draining the basin. It was expected that the seasonal runoff of the herbicides in the creek affected the sensitivity of the periphyton in accord with the rationale of the Pollution Induced Community Tolerance (PICT): the exposure of the community to pollutants result in the replacement of sensitive species by more tolerant ones. In this way, PICT can serve to establish causal linkages between pollutants and the observed biological impacts. The periphyton presented significantly different sensitivities against terbuthylazine through the year in accord with the seasonal application of this herbicide in the crops nowadays. The sensitivity of already banned herbicides, atrazine and simazine does not display a clear seasonality. The different sensitivities to herbicides were in agreement with the expected exposures scenarios, according to the agricultural calendar, but not with the concentrations measured in water, which altogether indicates that the use of PICT approach may serve for long-term monitoring purposes. That will provide not only causal links between the occurrence of chemicals and their impacts on natural communities, but also information about the occurrence of chemicals that may escape from traditional sampling methods (water analysis). In addition, the EC50 and EC10 of periphyton for terbuthylazine or simazine are the first to be published and can be used for impact assessments.