Toward Sustainable Environmental Quality: Priority Research Questions for Asia

Environmental and human health challenges are pronounced in Asia, an exceptionally diverse and complex region where influences of global megatrends are extensive and numerous stresses to environmental quality exist. Identifying priorities necessary to engage grand challenges can be facilitated through horizon scanning exercises, and to this end we identified and examined 23 priority research questions needed to advance toward more sustainable environmental quality in Asia, as part of the Global Horizon Scanning Project. Advances in environmental toxicology, environmental chemistry, biological monitoring, and risk-assessment methodologies are necessary to address the adverse impacts of environmental stressors on ecosystem services and biodiversity, with Asia being home to numerous biodiversity hotspots. Intersections of the food-energy-water nexus are profound in Asia; innovative and aggressive technologies are necessary to provide clean water, ensure food safety, and stimulate energy efficiency, while improving ecological integrity and addressing legacy and emerging threats to public health and the environment, particularly with increased aquaculture production. Asia is the largest chemical-producing continent globally. Accordingly, sustainable and green chemistry and engineering present decided opportunities to stimulate innovation and realize a number of the United Nations Sustainable Development Goals. Engaging the priority research questions identified herein will require transdisciplinary coordination through existing and nontraditional partnerships within and among countries and sectors. Answering these questions will not be easy but is necessary to achieve more sustainable environmental quality in Asia. Environ Toxicol Chem 2020;39:1485-1505. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Partitioning and Bioaccumulation of Legacy and Emerging Hydrophobic Organic Chemicals in Mangrove Ecosystems

Knowledge regarding partitioning behavior and bioaccumulation potential of environmental contaminants is important for ecological and human health risk assessment. While a range of models are available to describe bioaccumulation potential of hydrophobic organic chemicals (HOCs) in temperate aquatic food webs, their applicability to tropical systems still needs to be validated. The present study involved field investigations to assess the occurrence, partitioning, and bioaccumulation behavior of several legacy and emerging HOCs in mangrove ecosystems in Singapore. Concentrations of synthetic musk fragrance compounds, methyl triclosan (MTCS), polychlorinated biphenyls, organochlorine pesticides, and polycyclic aromatic hydrocarbons were measured in mangrove sediments, clams, and caged mussels. Freely dissolved concentrations of the HOCs in water were determined using silicone rubber passive samplers. Results showed that polycyclic musks and MTCS are present in mangrove ecosystems and can accumulate in the tissues of mollusks. The generated HOC concentration data for mangrove water, sediments, and biota samples was further utilized to evaluate water-sediment partitioning (e.g., K_oc values) and bioaccumulation behavior (e.g., BAF and BSAF values). Overall, the empirical models fit reasonably well with the data obtained for this ecosystem, supporting the concept that general models are applicable to predict the behavior of legacy and emerging HOCs in mangrove ecosystems.

Use of a suite of biomarkers to assess the effects of carbamazepine, bisphenol A, atrazine, and their mixtures on green mussels, Perna viridis

The present study investigated the toxicity of several emerging contaminants: the pharmaceutical drug carbamazepine (CBZ), the plasticizer bisphenol A (BPA), and the herbicide atrazine (ATZ) in a marine bivalve. Green mussels (Perna viridis) were exposed to different concentrations of CBZ, BPA, and ATZ, either individually or as mixtures over a 7-d period, and a suite of molecular and cellular biomarkers were analyzed: biomarkers of immunotoxicity (total hemocyte count, phagocytosis, extracellular lysozyme), genotoxicity (Comet assay), neurotoxicity (inhibition of acetylcholinesterase [AChE]), endocrine disruption (vitellin-like proteins), and detoxification enzymes (cytochrome P4501A [CYP1A], 7-ethoxyresorufin O-deethylase [EROD], and glutathione-S-transferase [GST]). Results of the single-chemical exposure tests highlighted the relatively low toxicity of CBZ because most biomarker responses observed were recorded at concentrations well above environmental levels. Bisphenol A exposure at environmentally realistic concentrations resulted in clear immunomodulatory, genotoxic, and endocrine-disruptive effects. Similarly, 3 of the 10 biomarkers tested on green mussels (genotoxicity, inhibition of AchE, and EROD) responded after exposure to ATZ at environmentally relevant doses or below, and confirmed the potency of this herbicide to marine bivalves. Exposure tests using mixtures of CBZ, BPA, and ATZ also revealed that these 3 substances were generally acting in an additive manner on the selected biomarkers, at environmental doses, with some exceptions (antagonism and/or synergy) at low and high concentrations. The present study also confirms that most of the biomarkers used are suitable for biomonitoring studies with green mussels. Environ Toxicol Chem 2017;36:429-441. © 2016 SETAC.

Multi-tool assessment of trace metals in mangroves combining sediment and clam sampling, DGT passive samplers and caged mussels

The rapid loss of mangroves globally has triggered a call for a better understanding of this habitat, including its dynamics and the threats it is exposed to. The present paper reports the study of trace metals at nine mangrove sites in Singapore in 2012/2013, using the simultaneous application of various tools, namely sediment analyses, the technique of diffusive gradients in thin-films (DGT) and caged/native bivalves (for both chemical and biomarker analyses). DGT devices were successfully deployed over 28days in tropical mangrove waters, and the concentration measured with DGT showed significant correlation with the accumulation for Cu, Zn and Cd in caged mussels, and Cu for native clams, supporting the relevance of DGT to predict metal bioaccumulation. Concentrations in mangrove sediment are reported for As, Cd, Co, Cr, Cu, Ni, Pb and Zn. Sediment levels on a dry weight (dw) basis of Cu (ND-219.5μg/g dw) and Zn (ND-502μg/g dw) exceeded general sediment quality criteria at two sites. Most notably for these two metals, investigations based on the four tools (DGT, sediments, caged mussels and clams) were all able to segregate sites above and below the sediment quality guideline. This was further supported by a range of significant linear correlations between the measurements obtained with the various tools. The present findings support that these monitoring tools are comparable in the field to provide a time-integrated assessment of metals such as Cu and Zn.

Pharmaceutically active compounds and endocrine disrupting chemicals in water, sediments and mollusks in mangrove ecosystems from Singapore

This study investigated the occurrence of bisphenol A (BPA), atrazine and selected pharmaceutically active compounds (PhACs) in mangrove habitats in Singapore in 2012-2013, using multiple tools (sediment sampling, POCIS and filter feeder molluscs). Using POCIS, the same suite of contaminants (atrazine, BPA and eleven PhACs) was detected in mangrove waters in 28-days deployments in both 2012 and 2013. POCIS concentrations ranged from pg/L to μg/L. Caffeine, BPA, carbamazepine, E1, triclosan, sulfamerazine, sulfamethazine, and lincomycin were also detected in mangrove sediments from the low pg/g dw (e.g. carbamazepine) to ng/g dw (e.g. BPA). The detection of caffeine, carbamazepine, BPA, sulfamethoxazole or lincomycin in bivalve tissues also showed that these chemicals are bioavailable in the mangrove habitat. Since there are some indications that some pharmaceutically active substances may be biologically active in the low ppb range in marine species, further assessment should be completed based on ecotoxicological data specific to mangrove species.

Alumina nanoparticles enhance growth of Lemna minor

The industrial use of nanoparticles is rapidly increasing, and this has given rise to concerns about potential biological impacts of engineered particles released into the environment. So far, relatively little is known about uptake, accumulation and responses to engineered nanoparticles by plants. In this study, the effects of alumina nanoparticles on growth, morphology and photosynthesis of Lemna minor were quantified. It was found that alumina nanoparticles substantially increase biomass accumulation of L. minor. Such a stimulatory effect of alumina nanoparticles on growth has not been reported previously. Enhanced biomass accumulation was paralleled by morphological adjustments such as increased root length and number of fronds per colony, and by increased photosynthetic efficiency. Metal nanoparticles have previously been shown to enhance the energy transfer efficiency of isolated reaction centres; therefore it is proposed that the mechanism underlying the alumina mediated enhancement of biomass accumulation in L. minor is associated with increased efficiencies in the light reactions of photosynthesis.

In vivo exposure to microcystins induces DNA damage in the haemocytes of the zebra mussel, Dreissena polymorpha, as measured with the comet assay

The Comet assay was used to investigate the potential of the biotoxin microcystin (MC) to induce DNA damage in the freshwater zebra mussel, Dreissena polymorpha. Mussels maintained in the laboratory were fed daily, over a 21-day period, with one of four strains of the cyanobacterium, Microcystis aeruginosa. Three of the strains produced different profiles of MC toxin, while the fourth strain did not produce MCs. The mussels were sampled at 0, 7, 14, and 21 days by withdrawing haemocytes from their adductor muscle. In addition, a positive control was performed by exposing a subsample of the mussels to water containing cadmium chloride (CdCl(2)). Cell viability, measured with the Fluorescein Diacetate/Ethidium Bromide test, indicated that the MC concentrations, to which the mussels were exposed, were not cytotoxic to the haemocytes. The Comet assay performed on the haemocytes indicated that exposure to CdCl(2) produced a dose-responsive increase in DNA damage, demonstrating that mussel haemocytes were sensitive to DNA-damaging agents. DNA damage, measured as percentage tail DNA (%tDNA), was observed in mussels exposed to the three toxic Microcystis strains, but not in mussels exposed to the nontoxic strain. Toxin analysis of the cyanobacterial cultures confirmed that the three MC-producing strains exhibit different toxin profiles, with the two MC variants detected being MC-LF and MC-LR. Furthermore, the DNA damage that was observed appeared to be strain-specific, with high doses of MC-LF being associated with a higher level of genotoxicity than low concentrations of MC-LR. High levels of MC-LF also seemed to induce relatively more persistent DNA damage than small quantities of MC-LR. This study is the first to demonstrate that in vivo exposure to MC-producing strains of cyanobacteria induces DNA damage in the haemocytes of zebra mussels and confirms the sublethal toxicity of these toxins.

Impacts of microcystins on the feeding behaviour and energy balance of zebra mussels, Dreissena polymorpha: a bioenergetics approach

Microcystins are produced by bloom-forming cyanobacteria and pose significant health and ecological problems. To investigate the impacts of these biotoxins on the physiology of the zebra mussels, Dreissena polymorpha, a series of short-term feeding experiments were conducted in the laboratory. We used five microalgal diets consisting of single-cell suspensions of the green algae, Chlorella vulgaris, the diatom, Asterionella formosa, the cryptophyte, Cryptomonas sp. and two strains of the toxic cyanobacterium, Microcystis aeruginosa (strains CCAP 1450/06 and CCAP 1450/10). A sixth diet was a mixture of the diatom and the CCAP 1450/10 cyanobacterial strain. The low-toxicity strain CCAP 1450/06 contained 7.4 microg l(-1) of the MC-LR variant while the very toxic strain CCAP 1450/10 contained 23.8 microg l(-1) of MC-LR and 82.9 microg l(-1) of MC-LF. A flow-through system was designed to measure the following feeding parameters: clearance, filtration, ingestion and absorption rates. Ultimately the scope for growth (SFG) was determined as a net energy balance. We observed that mussels cleared the cyanobacterial species containing MC-LF (mean+/-95% confidence interval) at a significant lower rate (498+/-82 ml h(-1) g(-1) for the single cell suspension and 663+/-100 ml h(-1) g(-1) for the mixture diet) than all of the non-toxic species and the cyanobacterium containing MC-LR (all above 1l h(-1) g(-1)). The same pattern was observed with all the feeding parameters, particularly absorption rates. Furthermore, MC-LF caused an acute irritant response manifested by the production of 'pseudodiarrhoea', unusually fluid pseudofaeces, rich in mucus and MC-LF-producing Microcystis cells, ejected through the pedal gape of the mussels. This overall response therefore demonstrates selective rejection of MC-LF-producing cyanobacteria by zebra mussels, enhancing the presence of the very toxic MC-LF-producing M. aeruginosa in mixed cyanobacterial blooms and in the benthos. Finally, we observed that the SFG (mean+/-95% confidence interval) of mussels feeding on M. aeruginosa containing MC-LF was significantly lower (34.0+/-18.8 J h(-1) g(-1) for the single cell suspension and 83.1+/-53.0 J h(-1) g(-1) for the mixture diet) than for mussels ingesting non-toxic diets, except for C. vulgaris (all above 200 J h(-1)g(-1)). This reveals a sublethal, stressful effect of microcystins (particularly MC-LF) on the feeding behaviour and energy balance of the zebra mussel.

Pseudodiarrhoea in zebra mussels Dreissena polymorpha (Pallas)exposed to microcystins

Microcystins are produced by bloom-forming cyanobacteria and pose significant health and ecological problems. In this study we show that zebra mussels respond differently to different strains of Microcystis aeruginosa, and that a highly toxic strain causes zebra mussels to produce large quantities of mucous pseudofaeces, `pseudodiarrhoea', that are periodically expelled hydraulically through the pedal gape by shell valve adductions rather than by the normal ciliary tracts. Analysis of the pseudofaecal ejecta showed that the proportion of Microcystis aeruginosa relative to Asterionella formosa was high in the pseudofaeces and even higher in the `pseudodiarrhoea' when a mixed diet was given to the mussels. This confirms that very toxic Microcystis aeruginosa were preferentially being rejected by comparison with the non-toxic diatom in the pseudofaeces and even more so in the`pseudodiarrhoea'. Such selective rejection was not observed with low or non-toxic strains and would therefore tend to enhance the presence of toxic Microcystis aeruginosa in mixed Microcystis aeruginosacyanobacterial blooms, as well as transferring toxins from the water column to the benthos.

The observed acute irritant response to the toxin represents the first demonstration of an adverse sublethal effect of microcystins on invertebrate ecophysiology. Our results also suggest that it could be a specific response to microcystin-LF, a little studied toxin variant.

Genetic and physiological responses of flounder (Platichthys flesus) populations to chemical contamination in estuaries

We sampled and analyzed European flounder (Platichthys flesus) from two highly contaminated estuaries (Seine and Loire, France) and one moderately contaminated estuary (reference site: Ster, France). Significant and convergent modifications of the allelic frequencies for the loci phosphoglucomutase (PGM), glucose phosphate isomerase 2 (GPI-2), mannose phosphate isomerase (MPI), and aspartate aminotransferase (AAT-2) were evident for fish in the contaminated sites versus fish from the reference site. Back-calculation from otoliths showed that the average growth rate of fish between the first and the second winter was greater at the reference site (approximately 150 mm/year) than at the contaminated sites (approximately 100 mm/year). Flounder from the reference site also had a higher condition factor (somatic wt/(fish length)3) compared to fish from the two contaminated sites. However, the observed pattern of growth rate and condition factor might be biased by particular environmental conditions other than contaminants and must be confirmed by more extensive study. Flow cytometry analysis of fish blood revealed a significant difference in the frequency of abnormal profiles for fish from the Seine (20%) versus from the Ster (3%). We interpret this result as a marked genotoxic effect of contaminants on fish in the Seine system. Some genotypes, such as PGM 85/85, appeared to be linked to the measured components of fitness, particularly to DNA integrity. Thus, these genotypes might be considered to be more tolerant to pollutants. The frequency of the PGM 85 allele was clearly elevated in flounder from the more contaminated sites, compared to flounder from the reference site.