Mycofiltration of Aqueous Iron (III) and Imidacloprid Solutions, and the Effects of the Filtrates on Selected Biomarkers of the Freshwater Snail Helisoma duryi.

To alleviate the burden of water contamination, a newly developed form of bioremediation known as mycofiltration can be employed. Mycofiltration is an environment-friendly technology involving the treatment of contaminated water by passing it through a network of saprophytic fungal mycelium. A mycofilter made of Pleurotus ostreatus was used for the removal of iron (III) and imidacloprid from aqueous solutions. Batch mycofiltration, at a dosage of 1 g of mycofilter per 50 mL, was performed on iron (III) solutions of different concentrations (0.99, 10.7, 22.9, and 27.72 mg/L) and pH (3.3, 7 and 11). For column mycofiltration, the mycofilter was packed into pyrex columns (3.3 × 15 cm) to desired bed heights. Iron (III) and imidacloprid solutions of 18.99 mg/L and 234.70 ng/L, respectively, were filtered at a constant flow rate. Thereafter, Helisoma duryi snails were exposed for 96 h to the respective filtrates, and their catalase and acetylcholinesterase activities were assessed. Batch mycofiltration showed iron (III) removal rates as high as 85%. Column mycofiltration showed removal rates of 94 and 31% for iron (III) and imidacloprid, respectively. Catalase activity was significantly reduced (p < 0.05) in the snails exposed to iron (III) or imidacloprid filtrates, compared to the snails exposed to the non-mycofiltered media. A significantly higher acetylcholinesterase activity was induced by iron (III) filtrates in comparison with the non-mycofiltered media (p < 0.05). There were no significant differences in acetylcholinesterase activity (p > 0.05) in the snails exposed to mycofiltered and non-mycofiltered imidacloprid media. Mycofilter characterisation using Fourier Transform Infrared Spectrophotometry revealed significant changes in transmittance intensity in the mycofilters used for the iron (III) vs the ones used for the imidacloprid solutions. Mycofiltration was found to improve water quality although iron (III) was removed more effectively than imidacloprid.

Dietary deprivation reduces the deleterious effects of carbaryl on the survival and activity of both catalase and acetylcholinesterase in earthworms.

Dietary restriction (DR) and dietary deprivation (DD) have been shown to be significantly beneficial in terms of lifespan gains and stress alleviation in invertebrate and vertebrate species. Such beneficial effects, however, have yet to be clearly assessed in the presence of chemical stressors. We conducted a comparative evaluation of the toxicity of carbaryl in Eisenia fetida individuals subjected to a full diet (FD), DR and DD. For 14 days, groups of ten worms subjected to FD received 5 g oatmeal, those subjected to DR received 2.5 g oatmeal, and those subjected to DD received 0 g oatmeal weekly. We evaluated concentrations of 0, 7, 14 and 28 mg carbaryl.kg-1 soil and measured effects on survival, reproduction, biomass and biomarkers (Catalase- CAT and acetylcholine esterase- AChE). Carbaryl caused a total inhibition of reproduction in all the treatments. For each diet level, the 14-day LC50 s were higher than 28 mg.kg-1, but the 14-day LC20 s for the earthworms subjected to FD, DR, and DD were 11.24, 20.51 and > 28 mg.kg-1, respectively. This showed that the toxicity of carbaryl consistently decreased with the reduction in nutrients. Carbaryl caused a significant weight loss in the worms subjected to FD in the 7 mg.kg-1 treatment (P = 0.0065). Such weight loss was not found in any of the other treatments and diets. Both CAT and AChE were significantly inhibited in the two highest treatments (P = 0.0071 and P = 0.0073, respectively). Interestingly, the earthworms subjected to DD showed relatively lower biomarker inhibition, indicating a greater tolerance to oxidative and neurotoxic stresses in these starved earthworms. For all endpoints investigated, aside from reproduction, the starved earthworms fared better under carbaryl toxicity than those given the other diets. Overall, a positive correlation was observed between the amount of food and chemical toxicity as mortality rates, AChE and CAT inhibition increased with the increased amount of nutrients given to the worms. These results show that, in the presence of a chemical stressor, the beneficial effects of DR and DD were variably manifest for select lifecycle parameters and biomarker responses, further suggesting dietary reduction as a non-genetic intervention that could help extend lifespan and alleviate stress even under a chemical insult.

Trend relationship between mountain normalized difference vegetation index (NDVI) and aerosol optical depth (AOD) across two decades: implication for water quality within the Lesotho Highlands, Drakensberg, South Africa.

There are growing concerns on contribution of vegetation dynamics to atmospheric turbidity and quality of regional water towers. The study sought to determine the trends in the MODIS/TERRA-derived normalized difference vegetation index (NDVI) and aerosol optical depth (AOD) for Lesotho Highland over 2000-2020. The predictive relationship between the two variables was also examined using regression analysis. Irrespective of yearly AOD patterns, the AOD showed biphasic patterns peaking between mid-winter to early spring (July-October) (highest) and autumn (Feb-April) (next highest), and lowest in the summer (Nov-January). The monthly NDVI was largest in January-March (summer-early fall) with smaller values in winter and spring. This seasonality can be related to the peak of anthropogenic biomass combustion during the winter and strong winds during the spring and early summer. The AOD relationship with NDVI showed quadratic patterns peaking and plunging with changes in season. About 30-80% (R2 = 0.3-0.8%) changes in annual AOD from 2000 to 2020 were explainable by the dynamics of NDVI indicating that increased NDVI contributes to about a 50% decrease in AOD in the Lesotho Highlands. However, an outlier trend was observed in 2007 (R2 = 13%). Incidences of high AOD in months of high NDVI may be indicative of traveling aerosols, i.e., aerosols from non-local sources/activity. On the other hand, high AOD in months of low NDVI implicates local aerosol sources. Trend relationship studies on vegetation loss and AOD in mountain areas of other regions could improve knowledge of contaminant dynamics and risk implications for downstream populations.

Developmental performance of Eristalis tenax larvae (Diptera: Syrphidae): Influence of growth media and yeast addition during captive rearing.

In holometabolous insects, life-history characteristics can vary in response to diet. The main aim of this contribution was to examine which diet best promotes larval development and survival of the aquatic saprophagous hoverfly Eristalis tenax L. (Diptera: Syrphidae). This study was motivated by a need to optimize techniques for rearing these insects in captivity. We studied how adding yeast to several rearing media based on animal droppings or decaying plant material affected development and survival in captive larvae, and whether these effects could be optimized depending on the amount of yeast and the rearing medium. In addition, premature exit of larvae was examined in two medium volumes to investigate differences in pupation. Larvae in yeast supplemented rabbit growth medium pupated and emerged faster than those in horse and antelope growth media. A high number of adult females emerged when compared to males, and both seemed to have a shorter developmental period in yeast supplemented growth media. Pupal survival was significantly greater in a mixture of droppings and plant organic matter, and a high medium volume of 140 ml (p < 0.05). Between 10% and 17% of larvae prematurely exited the aquatic medium in high (140) and low (70 ml) medium volumes, respectively. These results provide additional information that may be crucial for the successful mass rearing of E. tenax in captivity, and suggest that apart from the addition of yeast, growth medium quality and volume may be limiting factors for the production of large colonies of adults.

Two novel bioassays useful for the quick assessment of chemical effects on the behavior of mosquito larvae (Culicidae) and adult earthworms (Lumbricidae).

The behavior, i.e., observable response of an organism can serve as a useful indicator of environmental quality. In the absence of death and other sublethal effects, behavioral changes can represent early warning signs of toxic effects. In the present contribution, we present two novel bioassays useful for the quick assessment of chemical effects on the behavior of mosquito larvae (Culicidae) and adult earthworms (Lumbricidae). These bioassays could have applications in ecological risk assessment and laboratory based ecotoxicological testing. The novel assays are:•A bioassay for the assessment of chemical toxicity on the swimming, breathing and resting behavior of Culicidae larvae.•A bioassay for the assessment of chemical toxicity on the escape behavior of Lumbricidae in water.•These bioassays were carried out using the systemic insecticide imidacloprid and documented the relatively rapid onset of the neurotoxic effects of imidacloprid to experimental organisms.

Behavioural changes and flight response of a mosquito (Culicidae) and an earthworm (Lumbricidae), respectively, after exposure to imidacloprid.

A major point of concern in ecotoxicology is the effects of pesticides on nontarget organisms. This can impact the ecological role played by certain beneficial species in nature. Regarding neonicotinoid insecticides such as imidacloprid (IMI), several measures, including limited trade, restrictive use, and ban have been implemented in Europe and the USA but not globally. The goal of our study was to evaluate the potential risk of this still widely used agrochemical on the behaviour of mosquito larvae (Culicidae) and the escape behaviour of earthworms (Lumbricidae). Changes in breathing, swimming and resting were recorded in mosquitoes postexposure to 0, 1 and 2 mg IMI/L for 10 min. Earthworms were topically exposed in water for 2 minutes to 0, 5, 10 and 20 mg IMI/L. The escape behaviour (initial escape distance and speed) of the earthworms were recorded. In culicids, resting particularly was significantly increased by the exposure to imidacloprid (p < 0.05). In earthworms, the initial escape distance was statistically longer (p < 0.05) when fleeing from the 5 mg IMI/L solution than the solutions with the two highest concentrations. The worms exposed to the 5 mg IMI/L reacted faster than those exposed to the higher concentrations, which explained the long distance covered in the same amount of time. These results point to the relatively quick onset of the neurotoxic effects of imidacloprid, crippling earthworms and altering the buoyancy of mosquito larvae. The ecological consequences of these findings on the completion of life cycles and the survival of these species in nature are yet to be established.

Laboratory assessment of the ecotoxic effects of sewage sludge from the Maluti-Drakensberg region on a terrestrial oligochaete species.

We used the Enchytraeid Reproduction Test to evaluate the potential ecotoxic effects of sewage sludge samples on terrestrial oligochaetes in an Afromontane area. The sludge samples were collected from two wastewater treatment plants near the towns of Phuthaditjhaba and Harrismith in the Afromontane region of the eastern Free State in South Africa. Laboratory experiments revealed that although the sludge samples were not detrimental to the survival of Enchytraeus albidus (p > 0.05); they were able to significantly hinder its reproduction (p < 0.01). Through metal analyses, the sludge samples were found to belong to the relatively "best quality" pollutant class a sludge which is deemed suitable for land disposal and use as soil amendment for agricultural purposes. Herein, we point to the fact that the current South African sewage sludge disposal guidelines may not insure the protection of beneficial soil dwelling invertebrates such as oligochaetes. Our contribution also highlights the paucity of studies with an emphasis on environmental pollution in mountain areas across Africa and should signal a need for broader environmental considerations such as environmental pollution to be taken into account in the existing mountain invertebrate conservation methodologies.

Preliminary evidence of differences in cadmium tolerance in metal-free stocks of the standard earthworm test species Eisenia andrei (Oligochaeta).

To test whether metal-tolerant and metal-sensitive earthworm specimens could be an inherent part of metal-free earthworm populations, (i) we used DNA barcoding to identify and categorize earthworms from 8 populations of the standard test species Eisenia andrei, and (ii) the earthworms carrying three of the identified COI haplotypes (named Hap1, hap3 and Hap3) were paired up and exposed to Cd in order to assess the difference in Cd sensitivity between the breeding pairs. A total of six breeding pairs were exposed to 0, 25, 50 and 100 mg Cd/kg for 4 weeks at 20 °C. The survival of the breeding pairs, their change in biomass and cocoon production were assessed. For all of the endpoints assessed, the results indicated that couple 6 (Hap3 × Hap3) was the most sensitive breeding pair whereas couple 4 (Hap1 × Hap3) was the least sensitive one. The analysis of Cd tissue contents revealed that with increasing Cd concentration, Cp6 (Hap3 × Hap3) could accumulate significantly more Cd than any other breeding pair (p ≤ 0.01). Our findings indicate that E. andrei may harbour intrinsically Cd-tolerant and Cd-sensitive individuals and that this may be due to individual differences in Cd accumulation kinetics. In the context of ecotoxicological testing, our results underline the importance of using genetically diverse populations in laboratory testing to prevent generating flawed data from genetically homogeneous laboratory stocks. Although we do not regard the present mitochondrial haplotypes as proxy for possibly nuclear encoded traits, we discuss the necessity of a standardised earthworm barcoding protocol that could help not only to confirm the taxonomy of laboratory earthworm stocks but also to select genetically diverse stocks suitable for laboratory testing.