Bioaccumulation capacity of Chlorella vulgaris and Spirulina platensis exposed to silver nanoparticles and silver nitrate: Bio- and health risk assessment approach

Human health risk assessment and uncertainty analysis of silver nanoparticles in water

Despite frequent detection in environmental waters, literature which quantifies the health risk of silver nanoparticles (Ag NPs) through oral ingestion is scarce. This study compiled literature data to find the removal of Ag NPs from different treatment schemes (i.e., natural, engineered, or hybrid). Ag NP concentrations were found either in surface water or in groundwater based on where the effluent of treatment schemes was discharged, i.e., either in surface water or in groundwater. Monte-Carlo simulation was carried out for probabilistic assessment of health risks for children for two hypothetical exposure scenarios: (a) ingesting river water while swimming and (b) drinking groundwater. Bio-accessible fraction, dietary metal adsorption factor, and concentrations of silver ions were incorporated to simulate realistic situations. Different treatment schemes were ranked for their nanoparticles' removal efficiency with respect to (i) exceedance probability from guideline value and (ii) health risk to children. Hybrid treatment combinations, i.e., conventional primary and secondary treatment units followed by nature-based units (constructed wetlands and soil aquifer treatment), were ranked the best. The health risk value was found to be less than 1, with the 99th percentile value less than 10-3 in all cases. The maximum allowable concentration of Ag NPs was found to be as low as 1.43 mg/L for groundwater, suggesting probable potential for risk. Uncertainty analysis revealed that the uncertainty of the influent NPs concentration in raw wastewater contributes > 99% to the variance of the hazard index. The results of this work indicate that the use of natural treatment technologies with existing engineered treatments provides higher nanoparticle removal from wastewater without the requirement of any tertiary treatment unit.

Accumulation and metabolization of the antidepressant venlafaxine and its main metabolite o-desmethylvenlafaxine in non-target marine organisms Holothuria tubulosa, Anemonia sulcata and Actinia equina

The assessment of exposure to the antidepressant venlafaxine and its major metabolite o-desmethylvenlafaxine in Holothuria tubulosa, Anemonia sulcata and Actinia equina is proposed. A 28-day exposure experiment (10 μg/L day) followed by a 52-day depuration period was conducted. The accumulation shows a first-order kinetic process reaching an average concentration of 49,125/54342 ng/g dw in H. tubulosa and 64,810/93007 ng/g dw in A. sulcata. Venlafaxine is considered cumulative (BCF > 2000 L/kg dw) in H. tubulosa, A. sulcata and A. equina respectively; and o-desmethylvenlafaxine in A. sulcata. Organism-specific BCF generally followed the order A. sulcata > A. equina > H. tubulosa. The study revealed differences between tissues in metabolizing abilities in H. tubulosa this effect increases significantly with time in the digestive tract while it was negligible in the body wall. The results provide a description of venlafaxine and o-desmethylvenlafaxine accumulation in common and non-target organisms in the marine environment.

Daphnia magna as biological harvesters for green microalgae grown on recirculated aquaculture system effluents

The sustainability of recycling aquaculture systems (RAS) is challenged by nutrient discharges, which cause water eutrophication. Efficient treatments for RAS effluents are needed to mitigate its environmental impacts. Microalgae assimilate nutrients and dissolved carbon into microbial biomass with value as feed or food ingredient. However, they are difficult to harvest efficiently. Daphnia magna is an efficient filter feeder that grazes on microalgae at high rates and serves as valuable fish feed. Combining nutrient removal by microalgae and biomass harvesting by D. magna could be a cost-effective solution for wastewater valorization. Nutrient removal from unsterilized aquaculture wastewater was evaluated using the microalgae species Chlorella vulgaris, Scenedesmus dimorphus, and Haematococcus pluvialis. The first two algae were subsequently harvested using D. magna as a grazer, while H. pluvialis failed to grow stably. All phosphorus was removed, while only 50-70 % nitrogen was recovered, indicating phosphorus limitation. Shortening the hydraulic retention time (HRT) or phosphorus dosing resulted in increased nitrogen removal. C. vulgaris cultivation was unstable at 3 days HRT or when supplied with extra phosphorus at 5 days HRT. D. magna grew on produced algae accumulating protein at 20-30 % of dry weight, with an amino acid profile favorable for use as high value fish feed. Thus, this study demonstrates the application of a two steps multitrophic process to assimilate residual nutrients into live feeds suitable for fish.

Uptake and depuration of three common antibiotics in benthic organisms: Sea cucumber (Holothuria tubulosa), snakelocks anemone (Anemonia sulcata) and beadlet anemone (Actinia equina)

Antibiotics are widely used drugs in human and veterinary medicine, which has attracted great attention in relation to the development of bacterial resistance, currently a problem of great concern for governments and states, as it is related to the resurgence of infectious diseases already eradicated. Understanding the bioaccumulation of antibiotics in aquatic organisms is an important key to understanding their risk assessment. The present study was designed to study the bioaccumulation of target antibiotics in relevant organisms inhabiting benthic marine environments. The uptake and elimination of ciprofloxacin (CIP), sulfamethoxazole (SMX) and trimethoprim (TMP) were investigated in sea cucumbers (Holothuria tubulosa), snakelock anemone (Anemonia sulcata) and beadlet anemone (Actinia equina) under controlled laboratory conditions. The results show that antibiotics have a particular trend over time during all periods of absorption and depuration. The tissue distribution of antibiotics in sea cucumber is strongly influenced by the structure of the compounds, while CIP is concentrated in the body wall; TMP is concentrated in the digestive tract. Two different approaches were used to estimate bioconcentration factors (BCFs) in different animal models, based on toxicokinetic data and measured steady-state concentrations. The BCF ranges were 456-2731 L/kg, 6-511 L/kg and 9-100 L/kg for TMP, CIP and SMX, respectively. The estimated BCF values obtained classify TMP as cumulative in A. equina and H. tubulosa, underlining the potential bioconcentration in these marine organisms. A correlation was observed between the BCFs of the target antibiotics and the octanol-water distribution coefficient (D_ow) (r² > 0.7). The animal-specific BCF followed the order of beadlet anemone > sea cucumber > snakelock anemone.

Ecotoxicological response of Spirulina platensis to coexisted copper and zinc in anaerobic digestion effluent

Copper ion (Cu²⁺) and zinc ion (Zn²⁺) are widely co-existent in anaerobic digestion effluent as typical contaminants. This work aims to explore how Cu²⁺-Zn²⁺ association affects physiological properties of S. platensis using Schlösser medium (SM) and sterilized anaerobic digestion effluent (SADE). Microalgae cells viability, biochemical properties, uptake of Cu²⁺ and Zn²⁺, and risk assessment associated with the biomass reuse as additives to pigs were comprehensively assessed. Biomass production ranged from 0.03 to 0.28 g/L in SM and 0.63 to 0.79 g/L in SADE due to the presence of Cu²⁺ and Zn²⁺. Peak value of chlorophyll-a and carotenoid content during the experiment decreased by 70-100% and 40-100% in SM, and by 70-77% and 30-55% in SADE. Crude protein level reduced by 4-41% in SM and by 65-75% in SADE. The reduction ratio of these compounds was positively related to the Cu²⁺ and Zn²⁺ concentrations. Maximum value of saturated and unsaturated fatty acids was both obtained at 0.3 Cu + 2.0 Zn (50.8% and 22.8%, respectively) and 25% SADE reactors (33.8% and 27.7%, respectively). Uptake of Cu in biomass was facilitated by Zn²⁺ concentration (> 4.0 mg/L). Risk of S. platensis biomass associated with Cu²⁺ was higher than Zn²⁺. S. platensis from SM (Cu²⁺ ≤ 0.3 mg/L and Zn²⁺ ≤ 4.0 mg/L) and diluted SADE (25% and 50% SADE) reactors could be used as feed additives without any risk (hazard index <1), which provides sufficient protein and fatty acids for pig consumption. These results revealed the promising application of using S. platensis for bioremediation of Cu²⁺ and Zn²⁺ in anaerobic digestion effluent and harvesting biomass for animal feed additives.