In situ aquatic bioassessment of pesticides applied on rice fields using a microalga and daphnids

Combined effect of copper sulfate and water temperature on key freshwater trophic levels - Approaching potential climatic change scenarios

This work relied on the use microcosms to evaluate the individual and the combined effects of different levels of copper sulfate (0.0, 0.013, 0.064 and 0.318mg Cu L^-1) - a fungicide commonly exceeding allowable thresholds in agricultural areas - and a range of water temperature increase scenarios (15, 20 and 25°C) on freshwater species belonging to different functional groups. Hence, the growth inhibition of primary producers (the microalgae Raphidocelis subcapitata and the macrophyte Lemna minor), as well as the survival and feeding behavior of a shredder species (the Trichoptera Schizopelex sp.) were evaluated. The results revealed that copper was toxic to primary producers growth, as well as shredders growth and survival, being the growth of L. minor particularly affected. Higher water temperatures had generally enhanced the growth of primary producers under non-contaminated (microalgae and macrophytes) or low-contaminated (macrophytes) conditions. Despite the tendency for a more pronounced toxicity of copper under increasing water temperatures, a significant interaction between the two factors was only observed for microalgae. Since the test organisms represent relevant functional groups for sustaining freshwater systems functions, the present results may raise some concerns on the impacts caused by possible future climate change scenarios in aquatic habitats chronically exposed to the frequent or intensive use of the fungicide copper sulfate.

On-site, serial exposure of female fathead minnows to the Elkhorn River, Nebraska, USA, spring agrichemical pulse

In the Midwestern United States, waterways such as the Elkhorn River experience an annual spring pulse of runoff that carries sediments, nutrients, and organic compounds downstream. The objective of the present study was to elucidate relationships between contaminant load in Elkhorn River water and biological impacts on female fathead minnows throughout the entire spring agrichemical pulse. Fish were maintained in on-site outdoor microcosms at the Elkhorn River Research Station. The start of the spring pulse was determined using commercially available atrazine strips that detected atrazine when concentrations exceeded 3 ppb. Once the pulse began, 5 serial 7-d exposures were conducted. Concentrations of atrazine, its metabolites, and 5 other herbicides were quantified using gas chromatography-mass spectrometry. Agrichemicals peaked during the first and second weeks of the pulse, with a smaller peak occurring during week 4, but the peaks were not directly associated with runoff events (as estimated from river discharge). Elevated agrichemical concentrations were associated with biological impacts, but not solely responsible. In the present study, differences in the abiotic environment were found to play a significant role in the defeminization of exposed female fathead minnows.

Immobilised Phaeodactylum tricornutum as biomonitor of trace element availability in the water column during dredging

This work reports changes of Cr, Cu, Zn, Cd, Hg and Pb concentrations in the dissolved fraction, suspended particulate matter and immobilised Phaeodactylum tricornutum Bohlin (Bacillariophyceae), as well as of microalgae specific growth rates, during a 5-month period dredging operation in a contaminated area of the Tagus estuary, Portugal. Trace element concentrations showed broad variations in the dissolved fraction and suspended particulate matter, presumably reflecting rapid exchanges of redox-sensitive elements between water and particles, in conjunction with the dilution effect caused by the tidal excursion. Immobilised cells exposed to dredging environmental conditions showed significantly higher concentrations of Cr, Cu, Zn, Cd, Hg and Pb than under no dredging conditions. Concomitantly, specific cell growth was significantly lower, suggesting that elements released with dredging affect the microalgae physiology. The results obtained in this in situ work imply that the dissolved fraction and the suspended particulate matter are relatively ineffective indicators of the trace element enhancement during dredging and pointed out immobilised P. tricornutum as a reliable and efficient biomonitoring tool for the assessment of trace element remobilisation.

Optimizing alginate beads for the immobilisation of Phaeodactylum tricornutum in estuarine waters

This study addresses the influence of calcium as hardening agent, on alginate gel bead stability and suitability for the growth of Phaeodactylum tricornutum Bohlin (Bacillariophyceae) in estuarine waters. Alginate beads produced with 1, 2, 4, 5 and 6% of CaCl2 solutions were investigated for stability and suitability for growth of P. tricornutum cells, under mean salinity 27, at 220 and 440 rpm stirring laboratory conditions, and in devices placed under in situ estuarine conditions. Gel stability and suitability for cell growth were evaluated through bead diameter, bead disruption, dissolution and loss of spherical shape, cell viability and specific growth rates. Beads gelled with 5% CaCl2 were found the most suitable to sustain gel stability and cell growth in the estuarine waters. These beads were surveyed during dredging operations in the Tagus estuary, both in situ and in estuarine water under laboratory conditions, showing significantly lowered growth rates possibly due to Mn, Co and As accumulated in the cells. Results confirmed that the monitoring tool presented is reliable and effective for the assessment of anthropogenic impacts.