Triclocarban and triclosan have been reported to be taken up by several crop species from hydroponic solutions. For example, after exposure to an aqueous solution mixture of triclocarban and triclosan 11 different food crops, cucumber, tomato, cabbage, okra , pepper , potato , beet, onion , broccoli, celery , and asparagus , were capable of taking up both compounds. However, translocation from roots to the aerial tissue was ≤1.9% for triclocarban and ≤ 3.7% for triclosan after 1 month of exposure . Similarly, Wu et al. found triclocarban and triclosan to have a translocation factor < 0.01 in four vegetables cultivated in a hydroponic solution with two initial exposure concentrations . In a greenhouse study, triclocarban and triclosan were taken up in radish, carrot, and soybeans from bio solid-amended soils and, the greatest concentration was observed in the carrot root after 45 d of treatment and decreased thereafter . However, in a three-year field study in which soils were amended with bio solids in accordance with Ontario providence agricultural practices, the concentration of triclosan and triclocarban in the plant tissues was relatively steady and low . Plants have also been shown to metabolize triclosan, forming 33 metabolites in horseradish cell cultures with the majority being phase II conjugates . Further, one transformation product of the triclosan, methyl-triclosan, has been widely detected in environmental samples and is known to have greater toxicity than the parent compound . Parabens are common preservatives used in cosmetics, and among the most commonly detected CECs in TWW and bio-solid. Parabens are of concern due to their endocrine disrupting potential . Parabens have been widely detected in surface waters and sediments . However,raspberry container knowledge of their behavior, uptake, and transformation in terrestrial systems is comparatively limited.
Methyl paraben was unstable in soil after application of bio-solids, with the maximum concentration of 14.1 µg kg-1 reached after 5 h and decreasing to < 1 µg kg-1 after 35 d . In a bio solid amended field, methyl paraben was the lone paraben detected in the bio solids but was not quantifiable in tomatoes, sweet corn, carrot and potatoes . The above studies highlight the potential for CECs to enter the terrestrial environment, accumulate in plant tissues, and undergo transformations in plants. However, the wide variations in plant uptake and translocation rates under different soil and environmental conditions are currently not well understood and warrant further investigation. Further, it must be noted that the majority of currently published studies have focused on many of the same 20 or so CECs and explored their uptake in mostly the same plant species . There are over 1500 pharmaceutical compounds, alone, currently in circulation . Further, many of the current models have been shown to overestimate the concentration of CECs in plant tissues . In addition, no models have been able to take into account plant metabolism when determining the concentration and risk of CECs in terrestrial plants. More research is needed on a wider swath of CECs with different physicochemical properties in a wider range of plants to improve risk assessment. Transformation of CECs in the environment, including through plant metabolism also needs to be further investigated to better understand their fate and risks in the terrestrial environment. Antibiotic exposure in plants has been widely studied due to previously observed phenotypic toxicity. Several studies showed decreases in root length and changes in shoot development of various plants exposed to several different classes of antibiotics including sulfamides, fluoroquinolones, and penicillins . Most of these studies were conducted at antibiotic concentrations greater than those of environmental relevance and/or utilized artificial or hydroponic growth media. For instance, shoot and root growth of pinto beans grown in a nutrient solution spiked with two antibiotics, chlortetracycline and oxytetracycline, significantly decreased in a dose-dependent manner . Enrofloxacin, a fluoroquinolone, induced hormetic and toxic effects on post-germination growth in lettuce, cucumber, radish and barley plants at concentrations ranging from 0.005 to 50 mg L-1 in laboratory conditions . Seed germination has also been studied as a potential biological end-point to assess toxicity to antibiotic exposure . The exposure effects on seed germination vary considerably by plant species and exposure chemical. In filter paper tests, sweet oat , rice and cucumber seeds were negatively impacted when the seeds were exposed to aqueous solutions of increasing concentrations of six antibiotics, i.e., chlortetracycline, tetracycline, tylosin, sulfamethoxazole, sulfamethazine, and trimethoprim .
The EC10 and EC50 for seed germination were, however, significantly different depending on the antibiotic and the plant species. Rice seeds exposed to sulfamethoxazole were the most sensitive with an EC10 of 0.1 mg L-1 but tylosin had an EC10 > 500 mg L.-1 On the other hand, cucumber seeds exposed to sulfamethoxazole had an EC10 > 300 mg L-1 but an EC10 of 0.17 mg L-1 for chlortetracycline . Exposure to antibiotics can also change plant nutrient and chemical compositions. For example, irrigation with water spiked with sulfamethoxazole and trimethoprim increased production in carbohydrate and soluble solid contents in tomatoes as compared to the plants irrigated with untreated water . The mechanisms driving the phytotoxicity of antibiotics have also been explored. Antibiotics can be directly toxic to or indirectly affect plants. Indirect adverse effects can arise from antibiotic exposure that detrimentally affects mycorrhizal fungi, a vital plant-microbe interaction . Direct toxicity can result when antibiotics interfere with plant hormones or chemical synthesis pathways, or damage chloroplasts, etc. For example, sulfamethoxazole was shown to directly disrupt the folate synthesis pathway in plants by blocking the action of dihydropteroate synthase . Tetracyclines was shown to interrupt mitochondrial proteostasis and damage plant chloroplasts . Interactions with plant hormones may also play a role in the observed phenotypic phytotoxicity. Erythromycin and tetracycline can promote the production of abscisic acid in plants . Abscisic acid, a stress hormone, is crucial for plant responses to drought, salinity, heavy metals, among other stressors , but antibiotic-induced production of this hormone can cause premature leaf and fruit detachment and inhibit seed germination. Plants, depending upon species, can also detoxify antibiotics through reactions with phase II metabolic enzymes . However, studies so far have shown significant variations among plant species. For example, the antibiotic chlortetracycline was detoxified by glutathione conjugation via glutathione-Stransferase in maize , but glutathione-S-transferase did not efficiently catalyze the conjugation in pinto beans . These detoxification reactions, likely produce a series of conjugated metabolites that have yet to be characterized. Understanding the extent of such conjugation is crucial for estimating the total antibiotic uptake, accumulation, and translocation of antibiotics in plants as the formation of conjugates may mask the total concentration, even though some of these conjugates may retain biological activity .
Several widely used NSAIDs, such as ibuprofen, acetaminophen, and diclofenac are amongst the most studied pharmaceuticals in the environment. Studies have shown that NSAIDs can induce toxicity to plants . Phytotoxicity, however, is often plant species and NSAID specific. For example, ibuprofen has been shown to inhibited root elongation in Sorghum bicolor at high concentrations, with EC50 of 232.64 mg L-1 . However,plastic plants pots in seed germination tests exposure to a hydroponic solution containing 1 mg L-1 ibuprofen, along with other fenamic acid class NSAIDs, increased the length of the primary root in lettuce but had no effect on radish . In the same study, diclofenac was observed to decrease the root-to-shoot ratio in radish seedlings cultivated in a sand/spiked-nutrient solution , but did not significantly affect the seed germination. However, protein content was not affected in maize cultivated in soils irrigated twice with different concentrations of acetaminophen but grain yields and seed germination were negatively impacted in a dose dependent-manner . Plants can metabolize and detoxify NSAIDs. For example, plants were found to detoxify acetaminophen by conjugation with glutathione followed by conversion to cysteine and acetylcysteine conjugates . Similarly, diclofenac was found to be converted to glucose conjugates in barley and horseradish and glutamic acid conjugates in Arabidopsis thaliana . Arabidopsis thaliana cell cultures can detoxify ibuprofen via conjugation with sugars and amino acids .As mentioned above, pharmaceuticals used to treat psychiatric disorders are another group of frequently detected pharmaceuticals in environmental samples, particularly the anticonvulsant carbamazepine . Carbamazepine exposure has been seen to exhibit mycotoxicity to carrot mycorrhizal endpoints by decreasing the production of fungal spores . Similarly, carbamazepine induced leaf necrosis, altered plant hormones and macronutrient concentrations, and reduced root growth at plant tissue concentrations of 1 to 4 mg kg-1 in zucchini cultivated in soil spiked with chemical at 0.1 – 20 mg kg-1 . Information on the toxicity of benzodiazepines and fluoxetine in terrestrial plants is still limited; however, toxicity has been reported in aquatic plantsfor these compounds, indicating that toxicity may also occur after exposure in terrestrial plants .Antimicrobials and preservatives are often added to personal care products to increase shelf life. They pass from the human body, largely unchanged, and ultimately end up in TWW, bio solids, and sewage sludge. . Antimicrobials and preservatives have been detected in agricultural soils after irrigation with TWW and/or the application of bio solids, and can be taken up by plants . Two antimicrobials, triclosan and triclocarban, have attracted more attention because of their potential for endocrine disruption and phytotoxicity . For example, triclosan significantly inhibited plant growth in cucumber and rice seedlings with EC50 of 108 mg kg-1 and 57 mg kg-1 , respectively . Lettuce shoot mass also decreased in a dose-dependent manner after cultivation in soil amended with triclocarban-spiked bio solids . On the other hand, growth of radish, carrot, soybean, spring wheat, and corn plants grown in soils amended with bio solids containing environmentally relevant concentrations of triclosan and triclocarban, improved compared to un-amended soils; likely due to the positive impacts of bio solids addition . Thus, plant species, concentrations, and growth media can significantly affect phytotoxicity of these CECs. Studies exploring the phytotoxicity of individual pharmaceuticals or classes of pharmaceuticals are useful to highlight high-risk compounds and/or the potential mechanism of toxicity.
CECs are, however, often introduced into the environment in complex mixtures and these mixtures can affect the uptake and translocation of individual compounds . Some studies report positive effects on plants exposed to CEC mixtures under environmentally relevant conditions. For instance, TWW irrigation increased tomato and lettuce yield compared to freshwater irrigation . Exposure of lettuce seedlings to a mixture of 11 CECs significantly altered plant metabolic pathways, including the citric acid cycle and pentose phosphate pathway, and decreased chlorophyll content in a dose-dependent manner . Also, exposure to 18 CECs at concentrations ranging from 5 to 50 µg L,-1 induced oxidative stress in cucumber seedlings and caused up regulation of enzymes associated with detoxification reactions . Literature on the toxicity of a number significant CECs to terrestrial plants is still very limited, and many of the studies have utilized concentrations that are orders of magnitude higher than those seen in the environment. Studies on the toxicity of mixtures in terrestrial plants are also limited, but warrant attention as several studies have indicated that mixtures can induce effects not observed from individual compounds . The ability of plants to detoxify these compounds through metabolism also merit further research. Overall, more research is needed on the toxicity of a wider range of CECs in plants under environmentally relevant conditions to more accurately assess the impacts of CECs in the agro-environment. The potential for exposure to, and toxicity of, CECs has been investigated in several aquatic invertebrate species. Toxicity end-points such as endocrine disruption, changes in growth, time to development, and mortality rates have been considered in these studies . Studies addressing the effects of CECs on terrestrial invertebrates are, however, few. Of the published studies on terrestrial invertebrates, the earthworm Eisenia fetida has been examined mainly due to their increased susceptibility and ecological importance . Literature pertaining to toxicities of various classes of CECs to terrestrial invertebrates is discussed below. Like in terrestrial plants, antibiotics can also induce toxicity in terrestrial invertebrates. Exposure to environmentally relevant concentrations of antibiotics caused mortality to earthworms and/or induced oxidative stress and genotoxicity in E. fetida. For instance, high concentrations of tetracycline and chlortetracycline inhibited antioxidant enzymes superoxide dismutase and catalase while these enzymes were stimulated at lower doses , and DNA damage was induced along a dose-dependent curve . Also, chlortetracycline can reduced juvenile earthworm and cocoon counts in E. fetida .