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An insight into the dynamic aspects of the accumulation process is essential for understanding bioaccumulation as well as effect studies of hydrophobic organic chemicals. This review presents an overview of kinetic studies with organisms (fish, bivalve, crustacean, insect, worm, algae, and protozoan) as well as passive samplers (solid and liquid phase microextraction, semipermeable membrane device, polymer sheet, solid-phase extraction, Chemcatcher, etc.) for the uptake of neutral nonpolar chemicals from the aqueous phase. Information about uptake rates, elimination rates, and 95% equilibration times was collected and analyzed with diffusion based models. The present literature review suggests that the surface to volume ratio appears to be a critical parameter for the uptake rate of the more hydrophobic chemicals both for samplers and organisms. In addition, as a very first approximation, the combination of the first-order kinetic model with the assumption that diffusion through the aqueous boundary layers is rate limiting, gives a reasonable description of the experimental kinetic data. In this way, the presented model might be used to estimate uptake and elimination rate constants of chemicals by organisms or passive samplers.

Nanoplastics (NPs; <0.1 μm) are speculated to be a bigger ecological threat due to their predicted wider distribution, higher concentrations, and bioavailability. Primary NPs are manufactured to be that size, while secondary NPs originate from fragmentation of bigger debris. To date, the long-term impact of NPs in freshwater systems, particularly secondary NPs, is not well-understood. Thus, we employed a freshwater invertebrate, Daphnia magna, to investigate the chronic effects of model primary NPs, fluorescent polystyrene nanospheres (PS-NPs; 20 nm), and water leachate of weathered single-use plastics that contained micro-and nanosized particles. In experiment 1, parent Daphnia (F0) were exposed to 1 and 50 mg/L PS-NPs until the production of the neonates (F1) followed by a two-generation recovery. PS-NPs were mainly detected in the intestine and brood chamber in F0 and transferred to F1 and F2. PS-NPs significantly decreased the appendage curling and heartbeat rate in F0 and reduced reproduction in F2. In experiment 2, the plastic leachate also reduced the appendage curling rate but increased growth and reproduction. The results suggest that the acute toxicity of primary and secondary plastic particles is low even at high concentrations, but their chronic and sublethal effects should not be overlooked.

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The suitability of traditional microbial indicators (i.e., Escherichia coli and enterococci) has been challenged due to the lack of correlation with pathogens and evidence of possible regrowth in the natural environment. In this study, the relationships between alternative microbial indicators of potential human fecal contamination (Bacteroides thetaiotaomicron, Methanobrevibacter smithii, human polyomaviruses [HPyVs], and F؉ and somatic coliphages) and pathogens (Salmonella spp., Pseudomonas aeruginosa, rotavirus, astrovirus, norovirus GI, norovirus GII, and adenovirus) were compared with those of traditional microbial indicators, as well as environmental parameters (temperature, conductivity, salinity, pH, dissolved oxygen, total organic carbon, total suspended solids, turbidity, total nitrogen, and total phosphorus). Water samples were collected from surface waters of urban catchments in Singapore. Salmonella and P. aeruginosa had significant positive correlations with most of the microbial indicators, especially E. coli and enterococci. Norovirus GII showed moderately strong positive correlations with most of the microbial indicators, except for HPyVs and coliphages. In general, high geometric means and significant correlations between human-specific markers and pathogens suggest the possibility of sewage contamination in some areas. The simultaneous detection of human-specific markers (i.e., B. thetaiotaomicron, M. smithii, and HPyVs) with E. coli and enterococcus supports the likelihood of recent fecal contamination, since the human-specific markers are unable to regrow in natural surface waters. Multiple-linear-regression results further confirm that the inclusion of M. smithii and HPyVs, together with traditional indicators, would better predict the occurrence of pathogens. Further study is needed to determine the applicability of such models to different geographical locations and environmental conditions. Indicator bacteria, such as Escherichia coli and enterococci (ENT), have been used extensively in past decades to indicate the presence of human enteric pathogens because of the great diversity of pathogens, the large volumes required, and the difficulty in concentrating the typically low concentrations of pathogens from water samples. In Singapore, microbial water quality guidelines for recreational freshwater currently target enterococci (less than 200 counts per 100 ml for 95% of the time).Despite the wide use of fecal indicator bacteria in microbial water quality monitoring, their suitability to represent a level of health risk is still being questioned. One of the reasons is the lack of data correlating the presence and concentrations of the indicators with the presence of disease-associated pathogens. With improvements in microbiological test methods and bacterial species identification, there is growing evidence that fecal indicator bacteria, including E. coli and ENT, do not necessarily correlate well with some of the enteric pathogens, particularly viruses (1). There is also evidence that E. ...

The thermal stability of antibiotics commonly detected in food is reviewed. To quantify degradation, 2 major techniques have been reported: liquid chromatography-based methods and microbiological tests. As the degradation products may also display some antimicrobial activity, microbiological tests may not be considered accurate analytical methods for quantifying antibiotic residues' degradation. Degradation percentages are summarized for different antibiotics and for various media (water, oil, milk, and animal tissues). Studies presented in the literature confirm that the thermal degradation of β-lactams, quinolones, sulfonamides, and tetracyclines can be described using a first-order kinetic model. Degradation rates, k, derived for this model for liquid matrix (water) at 100 °C, followed the general trend amongst antibiotic classes: β-lactams = tetracyclines (most heat-labile) > lincomycin > amphenicols > sulfonamides > oxfendazole > levamisole (most heat-stable). Although thermal processing results in a decrease in the concentration of parent antibiotic residues, degradation by-products have not been properly characterized to date. As some of these products were shown to be hazardous, further investigation is needed to determine their impact on food safety and human health. It is therefore currently difficult to definitively conclude whether or not antibiotic degradation during food processing is necessarily beneficial in terms of food safety.