Despite significant progress in understanding the toxicity of engineered nanoparticles (NPs) in aquatic environments, key gaps remain in our understanding of their uptake and effects on algae. Specifically, it is unclear whether NPs must be internalized and cross biological membranes to induce toxicity, or if surface interactions alone are sufficient. This study aimed to explore the relationship between uptake and effects of TiO2-NPs and CeO2-NPs on the green alga Raphidocelis subcapitata using advanced single-entity analytical techniques. Flow cytometry was used to distinguish algal cells from NP aggregates and determine growth rates, while single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS) quantified adsorbed and internalized metals, operationally discriminated by washing cycles with EDTA. Single-particle ICP-MS (SP-ICP-MS) characterized NP size distribution and dissolution. Results showed greater toxicity for CeO2-NPs (72h-EC50 of 13.6 ± 0.57 mg L⁻¹) compared to TiO2-NPs (72h-EC50 of 28.3 ± 1.16 mg L-1), with hormesis observed for TiO2-NPs between 11 and 20 mg L⁻¹. CeO2-NPs. induced a significantly higher level of ROS production, showing a 71.8 % increase compared to the unexposed control, whereas TiO2-NPs induced only a 39.46 % increase at highest tested concentration of 50 mg L-1. SC-ICP-MS revealed both adsorption and internalization of NPs, with Ti accumulation exceeding Ce, despite that CeO2-NPs induced stronger growth inhibition and oxidative stress. Hetero-aggregation between NPs and algae, along with changes in cell granularity, was observed at higher NP concentrations. These findings offer insights into TiO2-NPs and CeO2-NPs interactions with microalgae and highlight the importance of advanced analytical techniques in assessing nanoparticle behavior in aquatic ecosystems.

Methods to differentiate surface-bound and internalized Ag in phytoplankton are essential for understanding bioaccumulation but remain limited, especially for studies involving silver nanoparticles (AgNPs). To address this, we assessed biologically relevant ligands for extracting adsorbed Ag from Chlamydomonas reinhardtii and Cyclotella meneghiniana exposed to Ag⁺ or AgNPs, focusing on ligand type, concentration, and extraction time. Additionally, we examined the impact of these agents on AgNP stability and microalgal membrane integrity. The ligands l-histidine, l-glutamine, l-cysteine, and d-penicillamine were tested. The thiol-containing d-penicillamine, tested for the first time, showed the highest efficiency in desorbing Ag+ from Ag+-treated cells, followed by l-cysteine. Optimal conditions were 1 mmol L⁻¹ ligand concentration and 5 min contact time. For AgNP-exposed cells, two sequential cell resuspensions in Ag-free medium were sufficient to detach loosely bound AgNPs. Then, hydrogen peroxide (H2O2), a biologically relevant oxidant, was introduced for the first time in the extraction procedure to facilitate the oxidative dissolution of nanoparticles. A combination of 0.5 mmol L-1 H2O2 with a 1 mmol L-1l-cysteine or d-penicillamine effectively removed Ag from the cell walls of C. meneghiniana and C. reinhardtii. The tested extraction agents did not affect unexposed phytoplankton cells. However, AgNP-exposed cells treated with H2O2 showed slightly increased cell membrane damage in diatoms. A dissolution of AgNP was found in the presence of l-histidine and d-penicillamine and H2O2. These findings highlight the need to develop species-specific washing methodologies in AgNPs bioaccumulation studies and provide insight into optimized extraction methods for assessing AgNP adsorption, internalization, and toxicity.

Phytoplankton species influence mercury cycling through bioaccumulation and Hg(II) reduction, however their contribution to oxidation of Hg(0) in aquatic systems remains largely overlooked. The present study aims at investigating the oxidation of Hg(0) by two phytoplankton species: the diatom Cyclotella meneghiniana and the green alga Chlamydomonas reinhardtii. The algae were exposed to gaseous Hg(0) at concentrations in the range of 6-12 μg m-3, representative for contaminated environments, under various experimental conditions (open vs. closed systems, light vs dark, and alive vs dead cells). The obtained results revealed, for a first time, that Hg(0) oxidation in C. meneghiniana cultures was light-dependent and limited to live cells, whereas C. reinhardtii maintained similar oxidation rates in both live and dead cells. C. reinhardtii cultures exhibited nearly tenfold higher Hg(0) oxidation efficiency than C. meneghiniana, demonstrating a strong species-dependent effect. Both species facilitated Hg(0) uptake from air into water, demonstrating a potential route for atmospheric Hg(0) to enter aquatic food webs. This novel evidence of phytoplankton-mediated Hg(0) oxidation highlights the importance of species identity and environmental conditions in governing Hg transformations and bioavailability. The results could have significant implications for understanding mercury bioaccumulation and toxicity in aquatic ecosystems. Further research is needed to clarify their contribution to Hg(0) oxidation in aquatic systems and to elucidate the underlying mechanisms driving the process.

Antimony (Sb) mobility in soils, whether dissolved or colloidal, is an emerging concern, yet its geochemical behavior, particularly under future climatic conditions, remains poorly understood. In a 28-day microcosm experiment, we investigated Sb release from two shooting range soils under flooded conditions at 20°C and 25°C. Sequential extractions and pore water analyses were conducted to assess Sb release at different temperatures. Sb size distribution was examined across pore water filtrates and characterized using asymmetric flow field-flow fractionation (AF4). The soils had different levels of Sb (58 ± 9 and 422 ± 53 mg kg-1) and Pb (2.0 ± 0.9 and 14.1 ± 3.0 g kg-1) pollution and microbial biomass (microbial carbon: 1005 ± 48 and 196 ± 62 mg kg-1), which greatly affected Sb release. Elevated temperature decreased Sb release in the less contaminated soil with higher microbial biomass (max: 85 ± 4 vs. 125 ± 3 µg L-1), but increased it in the more contaminated soil with lower microbial biomass (max: 492 ± 10 vs. 410 ± 11 µg L-1). This contrast was attributed to differences in soil microbial biomass, which impacted the effect of temperature on microbially-mediated redox processes, such as the reduction to less mobile SbIII. A substantial fraction (13-36 %) of total soil pore water Sb was released as colloids (0.02-10 µm). AF4 analysis identified two colloidal Sb populations: organic colloids or Sb microcrystals (∼2.5 nm) and mineral nanoparticles (15-20 nm). This study underscores the microbial control of redox transformations and Sb release and provides new evidence on the importance of colloidal transport of Sb.

Silver nanoparticles (AgNPs) are increasingly used in various consumer products and industrial applications, raising concerns about their environmental impact on aquatic ecosystems. This study investigated the physicochemical stability, trophic transfer, and toxic effects of citrate-coated AgNPs in a freshwater food chain including the diatom Cyclotella meneghiniana and the gastropod Lymnaea stagnalis. AgNPs remained stable in the exposure medium, with a minimal dissolution (<0.06%) after 24 h, indicating that particulate forms dominated during exposure. AgNPs inhibited the growth of C. meneghiniana without significantly affecting chlorophyll-a content or reactive oxygen species (ROS) production. Scanning electron microscopy revealed extracellular polymeric substance (EPS) secretion, which likely formed eco-coronas, reducing AgNPs bioavailability and oxidative damage. However, trace element analysis showed significant depletion of iron, manganese, and nickel, indicating early metabolic stress and redistribution of essential metals to support antioxidant defenses. In L. stagnalis, toxicokinetic analysis showed distinct patterns of Ag uptake and depuration across exposure routes. Waterborne and foodborne exposure resulted in similar and higher Ag accumulation compared to the combined group. Waterborne exposure showed the highest non-eliminable fraction and a bioconcentration factor (BCF) > 1, indicating efficient uptake and retention. Foodborne exposure exhibited a biomagnification factor (BMF) > 1, despite efficient elimination. Combined exposure had the highest depuration rate, with BCF >1 and BMF <1, reflecting reduced trophic transfer potential. Oxidative stress in L. stagnalis was highest during combined exposure, with increased ROS in hemolymph during uptake. Foodborne exposure caused prolonged immune stress, evidenced by elevated total antioxidant capacity (TAC) and protein levels. In the hepatopancreas, foodborne exposure during depuration led to increased lipid peroxidation and TAC, indicating oxidative and metabolic challenges specific to dietary exposure. These results highlighted the complex interactions of AgNPs with primary producers and consumers in freshwater ecosystems, emphasizing the need for multi-route assessments in nanoparticle risk evaluations.

Phytoplankton are traditionally viewed as simple bioaccumulators and key entry points for mercury (Hg) into aquatic trophic chain. However the more recent findings suggest that they can function as dynamic biological systems capable of enhancing Hg cycling reactivity and altering its speciation. Nevertheless, the role of phytoplankton species in mercury transformations remains largely overlooked. The present study examined inorganic mercury (Hg(II)) methylation, monomethylmercury (MeHg) demethylation, and the production of dissolved gaseous mercury (Hg(0)) following exposure to sub-nanomolar concentrations Hg(II) or MeHg, representative of contaminated environments. Diatom Cyclotella meneghiniana was selected as a representative phytoplankton species due to its widespread presence in diverse aquatic ecosystems. To track transformation pathways, isotopically labeled Hg species were used to distinguish between methylation and demethylation processes. The results demonstrated rapid accumulation of both Hg(II) and MeHg in the diatom cells. A cellular demethylation of MeHg into Hg(II), primarily occurring within the cell debris fraction, but no detectable Hg(II) methylation was observed. The reduction of Hg(II) to Hg(0) was found to be biologically mediated and independent of the photosynthetic system. No significant production of Hg(0) after MeHg exposure was determined. Overall, these findings imply that phytoplankton species could actively contribute to mercury cycling in aquatic environments through cellular transformation processes, including MeHg demethylation and Hg(II) reduction.

Generating appropriate ecological risk assessments to support the rapid growth of nanotechnology requires a comprehensive understanding of the potential effects of engineered nanomaterials (ENMs), both toxic and beneficial, and accurate predictions of their environmental concentrations. While significant data exists for widely used nanomaterials, there remains a critical knowledge gap regarding the environmental and biological impacts of emerging ENMs, including graphene oxide, nanodiamonds, carbon nanotubes, and less common metal and metal oxides. This review aims to synthesize current knowledge on the ecological risks of emerging ENMs in aquatic environments. The concentrations are likely to be below common toxicological endpoints. In addition, for some of them there is the potential for hormesis: a beneficial dose that promotes growth of the organisms. Novel approaches, such as the "omics," can elucidate these effects. The review identifies key knowledge gaps, such as the necessity for better information on the effects of nanomaterial mixtures and the potential effects of organisms on the fate of ENMs, as well as for better models for estimating biomagnification. While the integration of artificial intelligence will serve to close these knowledge gaps, more standardized toxicity testing protocols are required to expand the number of studies that can be used to train machine learning models.

The influence of inorganic mercury (Hg(II)) exposure on photosynthetic microorganisms and their pigments remains understudied. Here, we employed resonance Raman (RR) spectroscopy to investigate the responses of two freshwater phytoplankton species, the green alga Chlamydomonas reinhardtii and the diatom Cyclotella meneghiniana to Hg(II) exposure. We selectively recorded the spectral RR signature of carotenoids in intact cells exposed to concentrations of 10 nM and 100 nM of Hg(II), representative for contaminated environment and unexposed control cells. A two-hour exposure of C. reinhardtii resulted in a slight decrease in lutein and beta-carotene levels, while total carotenoids RR band broadening, as revealed by the FWHM of the upsilon(1)(C=C) stretching mode from averaged RR spectra, suggested conformational changes in pigments. Higher Hg(II) concentration induced more pronounced conformational changes. Similarly, a two-hour exposure of C. meneghiniana resulted in slight decreased level of the fucoxanthin, while diadinoxanthin showed an opposite trend compared to control: when fucoxanthin decreased, diadinoxanthin increased under 10 nM Hg (II) exposure. At higher concentrations, the decrease in fucoxanthin was less pronounced, accompanied by a broadening of the band area, (with FHHM increased), indicating possible conformer occurrence in response to Hg-induced stress. The changes in the main carotenoid species of the two algae are species-specific, Hg(II) concentration-specific, and dependent on exposure time. The calculated spectral differences in absorbances from UV-VIS spectra of methanol extracts from each group supported the main findings obtained by RR, though with caution due to the selective extraction efficiency of the respective carotenoids. This study highlighted for a first time the capability of single-cell RR spectroscopy as a valuable tool for toxicity assessment and for comprehending early-stage alterations in carotenoid metabolism due to toxic metal exposure in vivo.

Mercury is a hazardous pollutant of global concern. While advances have been made in identifying the detri-mental effects caused by Hg species in phytoplankton, knowledge gaps remain regarding the metabolomic perturbations induced by inorganic mercury (Hg(II)) and monomethylmercury (MeHg) in these organisms. Di-atoms represent a major phytoplankton group essential in various global biogeochemical cycles. The current study combined targeted metabolomics, bioaccumulation, and physiological response assays to investigate metabolic perturbations in diatom Cyclotella meneghiniana exposed for 2 h to nanomolar concentrations of Hg(II) and MeHg. Our findings highlight that such exposures induce reprogramming of the metabolism of amino acids, nucleotides, fatty acids, carboxylic acids and antioxidants. These alterations were primarily mercury-species dependent. MeHg exposure induced more pronounced reprogramming of the metabolism of diatoms than Hg (II), which led to less pronounced effects on ROS generation, membrane permeability and chlorophyll concen-trations. Hg(II) treatments presented distinct physiological responses, with more robust metabolic perturbations at higher exposures. The present study provides first-time insights into the main metabolic alterations in diatom C. meneghiniana during short-term exposure to Hg species, deepening our understanding of the molecular basis of these perturbations.

Mercury is a highly toxic trace metal that can accumulate in aquatic ecosystems and when resent at high concentrations can pose risks to both aquatic life and humans consuming contaminated fish. This research explores the use of the metalloregulatory protein MerR, known for its high affinity and selectivity toward mercury, in a novel application. Through a cell surface engineering approach, MerR was displayed on cells of green alga Chlamydomonas reinhardtii. A hydroxyproline-rich GP1 protein was used as an anchor to construct the engineered strains GP1-MerR that expresses the fluorescent protein mVenus. The surface engineered GP1-MerR strain led up to five folds higher Hg2+ accumulation compared to the WT strain at concentration range from 10-9 to 10-7 M Hg2+. The binding of Hg2+ via MerR was specific and did not get significantly affected by major freshwater water quality variables such as Ca2+ and dissolved organic matter. The presence of other trace metals (Zn2+, Cu2+, Ni2+, Pb2+, Cd2+) in a same concentration range even resulted in 30-40 % increase in the accumulated Hg. Further, the engineered cells also demonstrated the ability to accumulate Hg2+ from the water extracts of the Hg-contaminated sediment samples. These results demonstrate a novel approach utilizing the cell surface display system in C. reinhardtii for its potential application in bioremediation.

Mercury (Hg) is a priority pollutant of global concern because of its toxicity, its ability to bioaccumulate throughout the food web and reach significant concentrations in top predators. Phytoplankton bioconcentrate large amounts of Hg and play a key role in the entry of Hg into the aquatic food web. However, the subcellular distribution of Hg in freshwater phytoplankton, known to affect it toxicity and trophic transfer is understudied. The present study aimed at investigating the accumulation of inorganic Hg (iHg) and its subcellular distribution in freshwater phytoplankton species. To this end green alga Chlamydomonas reinhardtii and diatom Cyclotella meneghiniana were exposed to 10 and 100 nM of iHg for 2 h. The concentrations of Hg in the adsorbed, intracellular and subcellular (granules, debris, organelles, heat -stable peptides (HSP) and heat-denaturable proteins (HDP)) fractions were determined. The results showed that C. meneghiniana accumulated more Hg compared to C. reinhardtii at both iHg exposure concentrations (10 nM: 4.41 +/- 0.74 vs. 1.10 +/- 0.25 amol cell -1; 100 nM: 79.35 +/- 10.78 vs. 38.31 +/- 4.15 amol cell -1). The evaluation of the subcellular distribution of Hg, revealed that the majority of Hg was concentrated in the organelles fraction (59.7 % and 74.6 %) in the green algae. In the diatom, Hg was mainly found in the organelles (40.9 % and 33.3%) and in the HSP fractions (26.8 % and 40.1 %). The proportion of Hg in HDP fraction decreased in favor of the organelles fraction in C. reinhardtii when the exposure concentration increased, whereas the proportions in the debris and organelles fractions decreased in favor of HSP fraction in C. meneghiniana. This study provides pioneering information on the subcellular distribution of Hg within in freshwater phytoplankton, a knowledge that is essential to understand the toxicity and trophic transfer of Hg in contaminated aquatic environment.

Based on the up-to-date knowledge we critically discuss the current understanding of the influence of the compounds secreted by phytoplankton species on the fate of metal-containing engineered nanoparticles (ENPs) in aquatic settings. Different biomolecules, such as extracellular polymeric substances (EPS) and exometabolites play important, yet to elucidate, role in the dissolution, colloidal stability, transformations and biouptake of the ENPs and thus shape their behavior within the phycosphere. Phytoplankton secretions can also mediate the synthesis of ENPs from dissolved ions by reducing the metals ions and capping the newly formed ENPs. However, the environmental significance of this process remains to be demonstrated. Exposure to ENPs triggers changes in the secretion of the biomolecules. An improved understanding of the regulatory mechanism and exometabolite changes due to ENP exposure is essential for deciphering the ENPs-phytoplankton interactions. Unveiling the significance of secreted biomolecules in modulating the behavior of the metal-containing ENPs is central for understudying the phytoplankton-ENPs feedbacks, drivers of transformations of ENPs and their mechanisms in the aquatic environment.

The present study explores the capability of asymmetrical flow field-flow fractionation (AF4) coupled online with diode array (DAD), fluorescence detectors (FLD), multi-angle light scattering (MALS) and dynamic light scattering (DLS) to characterize silver nanoparticles (nAg) hetero-aggregates formed with diatoms derived extracellular polymeric substances (EPS). The content of EPS varied from 10.5 to 105 mgC L-1 and nAg were dispersed at 4 mg L-1 in a freshwater medium. Good recoveries (∼ 76.9 ± 8.4%) of nAg-EPS were obtained from AF4-DAD signals, but an anomalous elution was observed as EPS concentration increased: AF4 retention times decreased despite average gyration radii measured by MALS for nAg-EPS increased (from 16 nm to 24 nm), which suggests a change in the aggregation state, as evaluated by UV-Vis scans obtained from DAD. A regular Brownian relaxation of nAg-EPS was proven for each EPS concentration using these 2 detectors. The comparison of on-line and batch DLS measurements validated in addition, that no (dis)aggregation occurs upon injections. After a thorough comparison with classical AF4 using standards, the frit-inlet-AF4 was used. Slightly higher recovery (79.6±4.6 %) was obtained but similar deviation of nAg-EPS elution occurred, excluding the implication of membrane differential fouling of nAg-EPS /conditioning effects of EPS. The investigation of physico-chemical parameters controlling the Brownian relaxation of nAg-EPS suggests the influence of nAg-EPS structure and EPS loading. This study demonstrates the suitable use of AF4 coupled to multiple detectors to probe-out eco-corona formation and characterize polydisperse systems containing NPs, EPS and their hetero-aggregates in freshwaters, even under a non-ideal size-fractionation scenario.

Entanglement, often associated with the interaction of large marine plastics and larger animals, has not yet been reported in the context of microplastics (MPs) and small organisms. In this study, Daphnia magna was exposed to fibrous and fragmentary MPs at concentrations ranging from 1 to 1000 items/mL for 7 days. The results revealed that fibrous MPs tended to entangle with the second antennae and tail claws of D. magna, whereas fragmentary MPs merely adhered to the surface of the daphnids but do not exhibit entanglement. Additionally, the swimming speed and projected area of swimming trajectories of daphnids significantly decreased in the 100 items/mL group compared with the control. However, the occurrence of entanglement and slow swimming was less pronounced in the 1000 items/mL group due to the aggregation of fibrous MPs. Scanning electron microscopy revealed that D. magna possessed a rich spine structure on the surface of their bodies, particularly on their antennae and tails. The entanglement of D. magna by fibrous MPs resembled the action of manufactured "hook and loop". Overall, the results of this research revealed that entanglement is observed in small animals exposed to fibrous MPs, highlighting the direct biological effects of MPs beyond ingestion.

Extracellular polymeric substances from the diatom Cyclotella meneghiniana adsorb onto citrate-coated nAg, forming an eco-corona and reducing nanoparticle dissolution and aggregation.

Bioaccumulation of dissolved elemental mercury (DGM) by various organisms has been demonstrated, but no study has shown its uptake and sequestration by phytoplankton species. The present study aims to investigate the accumulation of mercury by phytoplankton species exposed to DGM. Diatoms (Cyclotella meneghiniana and Navicula pelliculosa) and green algae (Chlamydomonas reinhardtii and Haematococcus pluvialis) were exposed to constant high level of atmospheric gaseous Hg (similar to 7.7 mu g m(-3)). Total mercury concentrations (THg) in the medium (dissolved fraction) and algae cells (cellular fraction) were determined using cold vapor atomic fluorescence spectroscopy. Results revealed a partitioning of Hg(0) between the atmosphere and phytoplankton cultures, with THg predominantly found in the algae cells. THg in the algae cultures decreased in the order: C. reinhardtii > H. pluvialis > N. pelliculosa > C. meneghiniana. However, the cellular concentration (mol cell(-1)) decreased in the order: H. pluvialis > C. reinhardtii > C. meneghiniana > N. pelliculosa. These results highlight species specificity in Hg accumulation upon exposure to DGM, further linked to the phytoplankton surface area. Our findings reveal for the first time that phytoplankton species significantly influence the partitioning of atmospheric Hg(0) in aquatic environments, with important implications for the understanding of the aquatic mercury cycle.

Artisanal and small-scale gold mining (ASGM) is crucial to the livelihoods of close to 20 million people in over 80 countries, including 4-5 million women, mainly in rural areas with limited alternative economic prospects, particularly in developing countries. ASGM is largely informal, which can add to the challenge of addressing negative social and environmental effects including impacts on biodiversity. However, with proper guidance, ASGM can operate in a responsible manner, using cleaner production methods that minimize impacts on human health and the environment. This study presents and analyzes the interactions between ASGM and biodiversity based on new findings from 27 ASGM National Action Plans (NAPs) developed within the framework of Article 7 and Annex C of the Minamata Convention on Mercury, as well as a global literature review of more than 100 publications. In terms of key findings according to the literature reviewed, alongside other human occupation such as agriculture and industrial activities, ASGM also has an impact on the environment and biodiversity. The interrelationship between ASGM and biodiversity, including protected areas, is pervasive at every stage of ASGM operations, from extraction to mine closure, and generates significant impacts on the surrounding ecosystems. These impacts include, in descending order of most reported impacts: deforestation, soil degradation, chemical contamination of aquatic and terrestrial systems, and changes to the turbidity of watercourses. Tropical regions and key species such as amphibians and freshwater fish are among the most affected. Singly or combined, these environmental stressors lead to loss or deterioration of habitat and, by extension, indigenous biodiversity and ecosystem services. In addition, legal, institutional, and regulatory frameworks and related measures, inadequate or non-existent in some cases, may not necessarily support sustainable practices, often resulting in exploited sites abandoned without remediation, reclamation, rehabilitation, or restoration measures. To mitigate such impacts a key recommendation arising from the literature review is to strengthen the integration of the interrelationship between ASGM and biodiversity in the implementation of existing relevant national strategies, including those developed under the NAPs. The global literature review also highlights the importance of a multi-stakeholder, systemic approach combining the use of geospatial analysis, scientific and local knowledge, as well as the adaptation of the relevant frameworks, capacity building, and awareness raising. This approach can inform decision making with a view to developing sustainable initiatives that prevent and reduce the impacts of artisanal and small-scale gold mining on ecosystems, and that preserve biodiversity.

Silver in its various forms, including dissolved silver ions (Ag+) and silver nanoparticles (AgNPs), is a promising alternative to traditional antibiotics, largely used in livestock as feed additives and could contribute to the decrease and avoidance of the development of antibiotic resistance. The present study aims to assess the potential ecotoxicity of a silver-based nanomaterial (Ag-kaolin), the feed supplemented with the nanomaterial and the faeces since the latter are the ones that finally reach the environment. To this end, green alga Raphidocellis subcapitata was exposed to the extracts of Ag-kaolin, supplemented feed, and pig faeces for 72 h, along with Ag+ and AgNPs as controls for comparison purposes. Given the complexity of the studied materials, single-cell techniques were used to follow the changes in the cell numbers and chlorophyll fluorescence by flow cytometry, and the accumulation of silver in the exposed cells by single cell inductively coupled plasma mass spectrometry (SC-ICP-MS). Changes in cell morphology were observed by cell imaging multimode reader. The results revealed a decrease in chlorophyll fluorescence, even at low concentrations of Ag-kaolin (10 mu g L-1) after 48 h of exposure. Additionally, complete growth inhibition was found with this material like the results obtained by exposure to Ag+. For the supplemented feed, a concentration of 50 mu g L-1 was necessary to achieve complete growth inhibition. However, the behaviour differed for the leachate of faeces, which released Ag2S and AgCl