W. Tyler Mehler

Occurrence and distribution of sediment-associated insecticides in urban waterways in the Pearl River Delta, China

Sediment-associated pesticides, including organochlorine (OCP), organophosphate (OP), and pyrethroid insecticides, were analyzed in urban waterways in three cities (Guangzhou, Dongguan, and Shenzhen) in the Pearl River Delta (PRD), China. The OCPs represented 27.2% of the detectable insecticides in sediment, and chlordanes, DDTs, and endosulfans were the most frequently detected OCPs. The currently used insecticide chlorpyrifos was the only OP detected above the reporting limit (RL), with concentrations ranging from <RL to 100 ng g(-1) dry weight (dw). Additionally, pyrethroids were detected in all sediments with the sum pyrethroid concentrations ranging from 4.26 to 384 ng g(-1) dw and this represented 64.9% of the sum insecticide concentration. Despite their widespread use, no studies have been conducted investigating the occurrence and distribution of pyrethroids in China. As the first report of pyrethroids in urban waterways in China, the current study found cypermethrin was the most abundant insecticide detected in the PRD at concentrations ranging from 1.44 to 219 ng g(-1) dw. Spatially, sediment from more populous and urbanized areas (Shenzhen and Tianhe district in Guangzhou) had higher insecticide residues than less populous agricultural areas. In the more modernized city of Shenzhen, the OCPs were seldom detected, whereas more diverse patterns of pyrethroids were observed. Potential sources of these insecticides, especially the frequently detected pyrethroids, were most likely from pest control during urban landscaping maintenance and from abatement programs targeting mosquitoes and ants. Results suggested that a shift in application pattern and elevated urbanization increased accumulation of currently used insecticides like pyrethroids in sediment, and made them the predominate insecticides in the PRD urban waterways.

Toxicity of sediment-associated unresolved complex mixture and its impact on bioavailability of polycyclic aromatic hydrocarbons

Unresolved complex mixtures (UCMs) and polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in sediment originating from oil leaks, shipping, and other human activities and thus it is necessary to understand the role of UCM on sediment toxicity and PAH bioaccumulation. In the current study, lethal and sublethal effects of sediment-associated UCM were examined in two benthic invertebrates (Chironomus dilutus and Lumbriculus variegatus) using two spiked sediments. Results showed that UCM alone was toxic to the organisms and its toxicity was species-dependent. Approximately 1% of UCM in sediment caused 50% mortality in C. dilutus, which indicated UCM at environmentally relevant concentrations can directly cause sub-lethal and lethal effects to benthic invertebrates. Moreover, bioaccumulation testing of sediment-associated PAHs to L. variegatus showed that the addition of UCM to sediment at low concentration (0.01%) increased PAH bioavailability. These findings were further confirmed by assessing bioavailability using Tenax extraction. In contrast, high concentrations of UCM in sediment (0.5%) may have formed non-aqueous phase liquids, which served as an alternative sorption phase for PAHs and reduced PAH bioavailability. Understanding the role of UCM in the overall oil toxicity and its impact on other contaminants would improve risk assessment of sediments impacted by petroleum products in the future.

Joint toxicity of a pyrethroid insecticide, cypermethrin, and a heavy metal, lead, to the benthic invertebrate Chironomus dilutus

Insecticides and heavy metals are frequently detected in the environment, but few studies have assessed the joint toxicity of organic and inorganic contaminants. Joint toxicity of a pyrethroid insecticide, cypermethrin, and a heavy metal, Pb(2+), was evaluated in the present study. An antagonistic toxic response was observed when the benthic invertebrate Chironomus dilutus was simultaneously exposed to the two contaminants in both water and sediment exposures. Pre-exposure bioassays with midges were also conducted, and toxicity of cypermethrin was significantly reduced for midges that were pre-exposed to Pb(2+). In addition, the impact of Pb(2+) on the bioavailability of cypermethrin to midges was measured using Tenax extraction. No significant difference was noted in the amount of Tenax-extractable cypermethrin when different amounts of Pb(2+) were added to sediment. Results suggested that altered organism sensitivity may contribute to the observed antagonistic interaction between cypermethrin and Pb(2+), whereas the influence of changes in toxicokinetic processes such as uptake, biotransformation, and elimination on the joint toxicity should be further studied. Finally, the decreased toxicity of cypermethrin when simultaneously applied with Pb(2+) may be one reason for the overestimation of sediment toxicity by cypermethrin alone in field-collected sediment.

Identifying the causes of sediment‐associated contamination in the Illinois River (USA) using a whole‐sediment toxicity identification evaluation

Whole-sediment toxicity identification evaluation (TIE) techniques were employed on the Illinois River Complex (IRC), USA to identify the sources of sediment toxicity that may have contributed to the decline in benthic invertebrate populations. The TIE focused on three classes of contaminants: ammonia, metals, and organics. Sediment toxicity was assessed using the amphipod Hyalella azteca, and the focus of the TIE was on assessing spatial and temporal patterns of contamination. Past studies suggested that ammonia was the major source of contamination in IRC sediments. However, the present study suggested that polycyclic aromatic hydrocarbons (PAHs) were the primary contributor to sediment toxicity. Phase I testing showed 46% of the site trials (12 of 26) exhibited increased H. azteca survival (p < 0.05) with the addition of powdered coconut charcoal (organic amendment), whereas zeolite (ammonia amendment) and Resin Tech SIR 300 (cationic metals amendment) did not increase H. azteca survival. Phase II testing revealed PAH concentrations were high enough to cause the observed toxicity, confirming phase I results. Spatially, sediment toxicity as well as pore-water ammonia concentrations declined with distance downstream from suspected contaminant sources, indicating a potential dilution or remedial effect. Temporally, pore-water ammonia, metals, and PAH concentrations varied among sampling periods over an annual cycle for some sites near urbanized areas, while remaining temporally consistent at others. The results of the present study provide new information on the sources of toxicity within the IRC, and demonstrate the importance of evaluating spatial and temporal aspects in sediment TIEs. This is particularly important for evaluations in riverine systems in which hydrologic processes can result in large variation in sediment toxicity on temporal and spatial scales.

Influence of bioturbation on bioavailability and toxicity of PAHs in sediment from an electronic waste recycling site in South China.

The present study examined the effects of bioturbation by the oligochaete Lumbriculus variegatus on bioavailability and toxicity of sediment-associated polycyclic aromatic hydrocarbons (PAHs) to the oligochaete and the epi-benthic amphipod Hyalella azteca. Various densities of L. variegatus in sediment were used to represent different levels of bioturbation. Total sediment concentration declined with increasing worm density, but bioavailability of PAHs estimated using the biomimetic extractions showed no significant difference among treatments with different worm densities. Alternatively, PAH bioaccumulation by L. variegatus decreased and the growth of the worms was reduced at the highest worm density, which was probably due to overcrowding of organisms, food competition and increasing release of PAHs by bioturbation. Additionally, co-exposure with high density of L. variegatus to contaminated sediment significantly increased PAH accumulation and mortality of H. azteca. The increased toxicity was probably because of the transport of sediment-associated contaminants to sediment surface and water column by the bioturbation by L. variegatus. Overall, the present study showed that bioturbation may alter the toxicity of contaminants in sediment to other organisms, thus the presence of benthic invertebrates and their interactions with the sediment should be considered in future sediment risk assessment.

Comparative analysis of whole sediment and porewater toxicity identification evaluation techniques for ammonia and non-polar organic contaminants

Porewater and whole sediment toxicity identification evaluations (TIEs) were performed on contaminated Illinois River sediment and compared using two standardized toxicity-testing organisms (Ceriodaphnia dubia and Hyalella azteca). Results suggested that the choice of testing matrix (porewater versus whole sediment) significantly influenced characterization of toxicity. The porewater TIE suggested that ammonia was the major source of toxicity, while the whole sediment TIE indicated that non-polar organics, specifically polycyclic aromatic hydrocarbons, were the primary contributor to toxicity, with ammonia being a secondary contributor to toxicity. While the choice of test organism may have played a smaller role in the discordance between the TIEs, the data suggest that this factor alone could play a prevalent role in characterizing toxicity in other TIE assessments. Because porewater and whole sediment TIEs examine sediment toxicity differently, using both TIE approaches as part of a risk assessment may provide a more accurate risk estimate of sediment toxicity.

Effect-Directed Analysis of Toxicants in Sediment with Combined Passive Dosing and in Vivo Toxicity Testing

Identifying key toxicants in sediment is a great challenge, particularly if nontarget toxicants are involved. To identify the contaminants responsible for sediment toxicity to Chironomus dilutus in Guangzhou reach of the Pearl River in South China, passive dosing and in vivo toxicity testing were incorporated into effect-directed analysis (EDA) to account for bioavailability. Fractionation of sediment extracts was performed with gel permeation chromatography and reverse phase liquid chromatography sequentially. Polydimethylsiloxane served as passive dosing matrix for midge bioassays. The fractions showing abnormal enzymatic response were subject to a nontarget analysis, which screened out 15 candidate toxicants. The concentrations of the screened contaminants (log-based organic carbon normalized) in sediments of 10 sites were compared to sediment toxicity (10 and 20 day mortality and 10 day enzymatic response) to C. dilutus using correlation analyses. The results suggested that oxidative stress induced by cypermethrin, dimethomorph, pebulate and thenylchlor may have in part caused the observed toxicity to C. dilutus. The present study shows that EDA procedures coupled with passive dosing and in vivo toxicity testing can be effective in identifying sediment-bound toxicants, which may pose high risk to benthic organisms but are not routinely monitored and/or regulated. The findings of the present study highlight the importance of incorporating environmentally relevant approaches in assessing sediment heavily impacted by a multitude of contaminants, which is often the case in many developing countries.

Improvements and cost-effective measures to the automated intermittent water renewal system for toxicity testing with sediments

The push to make bioassays more sensitive has meant an increased duration of testing to look at more chronic endpoints. To conduct these longer bioassays through the use of traditional bioassay methods can be difficult, as many traditional bioassays have employed manual water changes, which take considerable time and effort. To that end, static-renewal systems were designed to provide researchers a technique to ease the manual water change burden. One of the most well-known static-renewal designs, the static intermittent renewal system (STIR) was produced by the United States Environmental Protection Agency in 1993. This system is still being used in laboratories across the globe today. However, these initial designs have become rather dated as new technologies and methods have been developed that make these systems easier to build and operate. The following information details changes to the initial design and a proof of concept experiment with the benthic invertebrate, Chironomus tepperi, to validate the modifications to the original system.

Evaluating freshwater mining sediment toxicity in Tasmania: Achieving strong multiple lines of evidence

Mining-impacted aquatic systems could be at risk from an assortment of pollutants. The present study evaluated toxicity of mining site sediments from western Tasmania by conducting bioassays with two Australian freshwater species (Chironomus tepperi and Austrochiltonia subtenuis). The present study used multiple lines of evidence (LoE) to assess risk to aquatic biota and the potential sources of that risk at these sites using a sediment quality guideline (SQG) comparison approach (i.e. comparing chemical concentrations at the site (in this case metals, sulfate, and acidic pH) to sediment guideline values) as well as a statistical approach (principle component analysis). Five of the nine mining site sediments showed significant toxicity to both species using survival (A. subtenuis and C. tepperi) and emergence (C. tepperi) as endpoints. Each LoE (SQG comparison and PCA analysis) provided a list of possible contaminants of concern for toxic sites, each list differing from one another. Evaluating these LoE collectively resulted in a stronger characterization of causality and reduced the potential contaminants of concern to a select few, including mainly: copper, sulfate, and acidic pH. Although using multiple lines of evidence reduced the number of potential contaminants of concern, the causality results were still not entirely conclusive, thus we also conducted preliminary investigations using toxicity identification evaluations (TIEs). These TIE investigations, showed the overall importance of acidic pH in these sediments, but also show the need for further work to improve the TIE technique for these types of sediment. The present study illustrates the strengths of using multiple LoE in assessing aquatic risk, especially in the assessment of complex sediments such as those in mining areas of Tasmania. The study, perhaps more importantly, also provides the foundation for more focused work to be conducted in the future to better understanding the implications of mining in western Tasmania.

Particle-scale understanding of cypermethrin in sediment: Desorption, bioavailability, and bioaccumulation in benthic invertebrate Lumbriculus variegatus

Influence of sediment particle size on the desorption, bioavailability, and bioaccumulation potential of cypermethrin was investigated in the present study using two biomimetic techniques (Tenax extraction and solid-phase microextraction (SPME)) and bioaccumulation testing with Lumbriculus variegatus. A field-collected sediment was wet sieved to obtain five particle-size fractions (<20, 20-63, 63-180, 180-500, and >500 μm) and used for cypermethrin spiking. The finest sediment (<20 μm) had the highest rapid desorption fraction (Fr) and rate (kr) when compared to coarser sediments. Elimination rate constants of cypermethrin determined by SPME (ke-SPME) and L. variegatus (ke-L.v.) for various fractions of sediments followed the same trend, suggesting SPME fiber acts as a good surrogate for benthic organisms considering passive partitioning. Finally, biota-sediment accumulation factors (BSAFs) of cypermethrin in worms were almost the same among the sediments with different particle sizes (0.425 ± 0.07-0.445 ± 0.07 g OC g-1 lipid), suggesting that the differences in desorption and freely dissolved concentrations of cypermethrin did not significantly influence its bioaccumulation potential in worms. Selective ingestion of fine sediment particles may be one of the contributing reasons for no differences in BSAFs observed in the treatments as would have been expected. The different desorption and freely dissolved concentrations of cypermethrin in sediments with different particle sizes observed in this study highlights the need for further work to better understand the influence of particle size on the toxicity of highly toxic insecticides, such as cypermethrin, to sensitive benthic species.