Andrew Ross Brown

Bioaccumulation studies performed as part of the environmental risk assessment of human pharmaceuticals are time- and resource-intensive, prompting interest in alternative nonanimal screening methods. For xenobiotics, including active pharmaceutical ingredients (APIs), biotransformation and metabolic clearance are key determinants of bioaccumulation and, consequently, effects in nontarget organisms like fish. Various in vitro liver models are available for studying pharmaceutical metabolism in fish, including microsomes, S9 fractions, and primary hepatocyte cultures maintained as suspensions, monolayers, or three-dimensional spheroids. However, broader application of these models is limited by a lack of robust in vitro-in vivo correlation data, as well as uncertainty regarding the most appropriate systems for different modeling purposes. This study critically evaluates in vitro liver models commonly used for assessing API clearance in fish, comparing their functionality, resource requirements, and informative value. Drawing on published data for selected APIs and on the strategies used to select suitable mammalian model systems, we propose the use of subcellular fractions for high-throughput screening of hepatic clearance (metabolic stability) and enzyme inhibition, hepatocyte suspensions for assessing intrinsic clearance while accounting for the impact of active drug transport, and hepatocyte monolayers or three-dimensional cultures for longer-term clearance and targeted effect studies. Key knowledge gaps are identified, and recommendations for future research are presented.

The Fish Plasma Model (FPM) predicts steady-state concentrations of active pharmaceutical ingredients (APIs) in fish blood plasma based on partitioning from the surrounding (water) environment. Total plasma concentration is then compared to the human therapeutic concentration to indicate environmental risk, assuming that human pharmaceutical targets are conserved in fish. However, only the unbound fraction (f_u) of API is available for pharmacological action and plasma protein binding, and the binding of APIs may differ between species. We quantify f_u for 44 APIs with wide ranging physicochemical properties in three fish species: a salmonid, rainbow trout (Oncorhynchus mykiss) and two cyprinids, fathead minnow (Pimephales promelas), and koi carp (Cyprinus rubrofuscus), and draw comparisons with f_u in humans. We examine interspecies differences in f_u in relation to blood physicochemistry and protein and lipid composition. We show that anionic APIs often exhibit substantially (×10) higher f_u in fish compared with humans, and this was most apparent in rainbow trout, despite this species possessing protein(s) orthologous to human serum albumin, a major binding protein for anionic APIs in humans. We recommend accounting for f_u in fish versus humans and using rainbow trout as a conservative species in the FPM for modeling API availability and effects in fish.

EcoDrug PLUS (EcoDrug+; https://ecodrugplus.helsinki.fi/) is a freely available and publicly accessible database, established to facilitate environmental risk assessment of pharmaceuticals and other bioactive substances, including veterinary medicines and pesticides. EcoDrug+ advancements on the original ECODrug database include a more extensive and intuitive graphical user interface for investigating the potential for chemicals to interact with protein targets based on their conservation with human drug, veterinary, and pesticide targets across 180 phylogenetically diverse wildlife taxa. EcoDrug+ integrates genomic and chemoinformatic data from open-access sources for ~7200 pharmaceuticals, 34 000 agrochemicals, 61 000 human metabolites, and 5800 other bioactive chemicals. Advanced search capabilities of EcoDrug+ include the ability to interrogate the database via text queries, chemical structure drawings, target protein sequence BLAST, and/or specified mechanisms of action. Chemical compound data are organized into clusters to facilitate the exploration of similar groups using interactive knowledge graphs. The integration of effects-based knowledge informs on appropriate endpoints and susceptible species for the testing of drugs (and other bioactive chemicals). Georeferenced measured environmental concentrations (for n = 266 chemicals) furthermore provide relevant exposure data for testing and environmental risk analysis.

Seaweed and shellfish aquaculture is increasing globally, offering potentially sustainable food sources with low environmental impacts and possible benefits, including habitat creation and restoration of degraded areas. Aquaculture siting in new areas often requires empirical evidence to support licencing applications; however, environmental impact assessments for seaweed and shellfish farms on underlying benthic (seabed) habitats are currently lacking. Here, we examined whether initiating kelp cultivation (predominantly Saccharina latissima ) in previous European lobster ( Homarus gammarus ) farming sites within a larger blue mussel ( Mytilus edulis ) farm influenced macrobenthic community structure and sediment composition in St Austell Bay, southwestern England, UK. After 2 seasons of kelp cultivation, no effects on sediment composition or macrofaunal abundance, biomass, diversity or assemblage composition were recorded. There was no significant difference in total macrofaunal abundance between M. edulis , H. gammarus or S. latissima culture areas; however, the aquaculture areas hosted higher macrofaunal abundance compared with reference areas outside the farm. Macrofaunal diversity did not differ between lobster/seaweed and reference areas, although it was significantly lower in mussel culture areas, corresponding with spatial variability in sediment composition over the ~70 ha site. Sediment composition was consistent within each treatment area over time, indicating no change due to the farm between 2017 and 2022. Overall, this study found that small-scale seaweed cultivation in a relatively dynamic and open coastal environment had minimal impacts on benthic communities after 2 growing seasons. More region-specific long-term surveys are recommended to confirm whether these findings apply to seaweed and mussel farming more widely.

Harmful Algal Blooms (HABs) can produce phycotoxins that accumulate in shellfish and subsequently poison aquatic predators and human consumers, potentially causing significant economic impacts to the shellfish aquaculture industry. HAB events are challenging to foresee as they are driven by complex inter‐annual and seasonal changes in physical, chemical and biological factors. Accounting for these environmental drivers and their interactions in statistical models allows for the development of HAB early warning systems. Typically, these have a forecasting horizon of 1–2 weeks, allowing shellfish businesses and regulators to increase monitoring intensity and take evasive action, including harvesting suspensions to protect consumer health. However, there is critical need for longer‐term predictions of risk, to enable more proactive mitigation, business planning, harvest scheduling and supply chain management. We present a statistical framework for providing seasonal‐scale early warnings of the occurrence and impacts of Dinophysis spp. HABs on shellfish aquaculture in Scotland, UK. We use penalized smooth functions of winter‐spring daily sea surface temperature to predict the severity and impact of ensuing summer blooms, including the percentage of toxicity measurements exceeding the harvesting closure threshold, as well as the anticipated start, end, and overall duration of closures. We illustrate the application of this framework to two Scottish aquaculture regions: One with a high spatial concentration of harvesting sites (Shetland) and one with more dispersed sites (West Scotland and the Hebrides). Through a comprehensive yearly prediction experiment, we demonstrate considerable skill in predicting the impact of unseen HAB seasons at a regional level.

The increasing levels and frequencies at which active pharmaceutical ingredients (APIs) are being detected in the environment are of significant concern, especially considering the potential adverse effects they may have on nontarget species such as fish. With many pharmaceuticals lacking environmental risk assessments, there is a need to better define and understand the potential risks that APIs and their biotransformation products pose to fish, while still minimizing the use of experimental animals. There are both extrinsic (environment- and drug-related) and intrinsic (fish-related) factors that make fish potentially vulnerable to the effects of human drugs, but which are not necessarily captured in nonfish tests. This critical review explores these factors, particularly focusing on the distinctive physiological processes in fish that underlie drug absorption, distribution, metabolism, excretion and toxicity (ADMET). Focal points include the impact of fish life stage and species on drug absorption (A) via multiple routes; the potential implications of fish's unique blood pH and plasma composition on the distribution (D) of drug molecules throughout the body; how fish's endothermic nature and the varied expression and activity of drug-metabolizing enzymes in their tissues may affect drug metabolism (M); and how their distinctive physiologies may impact the relative contribution of different excretory organs to the excretion (E) of APIs and metabolites. These discussions give insight into where existing data on drug properties, pharmacokinetics and pharmacodynamics from mammalian and clinical studies may or may not help to inform on environmental risks of APIs in fish.