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The extent to which chemicals bioaccumulate in aquatic and terrestrial organisms represents a fundamental consideration for chemicals management efforts intended to protect public health and the environment from pollution and waste. Many chemicals, including most pharmaceuticals and personal care products (PPCPs), are ionizable across environmentally relevant pH gradients, which can affect their fate in aquatic and terrestrial systems. Existing mathematical models describe the accumulation of neutral organic chemicals and weak acids and bases in both fish and plants. Further model development is hampered, however, by a lack of mechanistic insights for PPCPs that are predominantly or permanently ionized. Targeted experiments across environmentally realistic conditions are needed to address the following questions: (1) What are the partitioning and sorption behaviors of strongly ionizing chemicals among species? (2) How does membrane permeability of ions influence bioaccumulation of PPCPs? (3) To what extent are salts and associated complexes with PPCPs influencing bioaccumulation? (4) How do biotransformation and other elimination processes vary within and among species? (5) Are bioaccumulation modelling efforts currently focussed on chemicals and species with key data gaps and risk profiles? Answering these questions promises to address key sources of uncertainty for bioaccumulation modeling of ionizable PPCPs and related contaminants.

The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes. In this paper, we address the challenges and limitations facing current test methods and the scientific advances that are helping to both understand and provide solutions to them. Some of these advancements include the following: (1) robust methods that provide a deeper understanding of microbial composition, diversity, and abundance to ensure consistency and/or interpret variability between tests; (2) benchmarking tools and reference substances that aid in persistence evaluations through comparison against substances with well-quantified degradation profiles; (3) analytical methods that allow quantification for parent and metabolites at environmentally relevant concentrations, and inform on test substance bioavailability, biochemical pathways, rates of primary versus overall degradation, and rates of metabolite formation and decay; (4) modeling tools that predict the likelihood of microbial biotransformation, as well as biochemical pathways; and (5) modeling approaches that allow for derivation of more generally applicable biotransformation rate constants, by accounting for physical and/or chemical processes and test system design when evaluating test data. We also identify that, while such advancements could improve the certainty and accuracy of persistence assessments, th

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO2 and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO2 concentrations (ambient CO2: 360 ppm; medium CO2: 450 ppm; high CO2: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1 g Na/L) and cadmium nitrate (Cd(NO3)2·4H2O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO2 alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO2. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO2 stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO2. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.

Plant uptake of pharmaceuticals and personal care products (PPCPs) has been recognized as a potential path to human exposure. Most existing regressions and uptake models are limited to neutral organic compounds, but 80% of pharmaceuticals and an unknown number of personal care products ionize under environmentally relevant conditions. A widely used generic plant uptake model was expanded step-by-step with processes relevant for weak and strong acids and bases, such as ionization, membrane permeability, ion trap, phloem transport, and sorption to proteins. The differential equation system was solved analytically, and the equations were implemented in a spreadsheet version. The changes in predicted plant uptake of neutral substances, acids, and bases were found for a range of key input data (log KOW, pKa, pH, sorption to proteins). For neutral compounds, sorption to proteins and phloem transport are of relevance only for the more polar compounds (low log KOW, ≤2). Weak acids (pKa ≤6) are trapped in phloem due to pH-related effects, and in roots when pH in soil is low (pH 4–5). Cations sorb stronger and hence show less bioavailability and less translocation than anions. Sorption to proteins reduces translocation to leaves and fruits for all substances, but this is more evident for polar and ionic compounds that have negligible sorption to lipids. The new generic model considers additional processes that are of relevance for polar and ionizable substances. It might be used instead of existing standard approaches for chemical risk assessment and assessment of the environmental fate of PPCPs.

Most, if not all, chemicals, biocides, pharmaceuticals and pesticides are known to produce non-extractable residues (NER) in solid environmental media like soil and sediment during degradation testing to various extents. Since it has been found that parent substances and relevant metabolites can be contained and potentially released from NER there is currently much debate on how to include NER in the environmental persistence assessment. Using radioactive or stable isotope labelled test substances, three types of NER can be experimentally discriminated: entrapped, sorbed or heavily sorbed (type I) having the potential to be released from the matrix. Type II NER, i.e. residues covalently bound to organic matter in soils or sediments, are being considered to have very low remobilisation potential. Type III NER (bioNER) are formed after degradation of the xenobiotic chemical and incorporation into natural biomolecules (anabolism) like amino acids and other biomass compounds, and are, thus, of no environmental concern. Silylation has been suggested as a methodology to differentiate types I and II NER but concern has been addressed that this procedure is not suitable for routine analysis, e.g. in the context of studies for authorisation and registration of chemicals. Here, we describe a readily applicable and reproducible experimental procedure to apply this method for the analysis of NER derived from bromoxynil, sulfadiazine and isoproturon, respectively. This method is able to distinguish between heavily sorbed and covalently bound residues of chemicals, biocides, pharmaceuticals and pesticides in soils and to subsequently identify residues of the parent substance entrapped in type I NER.