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The combined pollution, instead of single pollution, has become a widespread contamination phenomenon in aquatic environment. However, little information is now available about the joint effects of the combined pollution, especially co-existed pesticides and heavy metals, on aquatic plants. In the present study, using continuous excitation chlorophyll fluorescence parameters and the OJIP transient, comparisons of herbicide atrazine (ATZ) phytotoxicity on Iris pseudacorus between in the presence and absence of cadmium (Cd) were evaluated over an exposure period of three weeks under laboratory conditions. Results showed that both ATZ and Cd were toxic to I. pseudacorus. The ratio Fv/Fo, specific electron transport energy (ET0/RC) and photochemistry efficiency (PIabs and PItotal) of this emergent plant species at individual ATZ and Cd concentrations were significantly lower than those of the control. ATZ mainly inhibited electron transport beyond QA at PSII acceptor side as indicated by the sharp rise of the J-step level of fluorescence rise kinetics. A pronounced K-step and the loss of I-step due to the damage on the OEC and PSI also occurred when ATZ was at or above 1.0 mg·L− 1. In comparison to ATZ alone, ATZ combined with Cd resulted in a lower amplitude rise in J-step with apparent J-I and I-P phases; and significantly lower Fo with higher Fv/Fo, as well as greater ET0/RC with higher values of PIabs and PItotal. However, the adverse influences of ATZ combined with Cd on the above indicators were still significant as compared with the control. Therefore, the coexistence of Cd alleviated the individual phytotoxicities of ATZ, whereas combined pollution of ATZ and Cd still induced the decline in photosynthetic performance of I. pseudacorus, and its potential ecological impacts on the aquatic vegetation cannot be ignored. Our findings offer a better understanding of the joint effects of the pesticide and heavy metal on non-target aquatic plants, and provided valuable insights into the interaction of these pollutants in aquatic environment.

Pesticide loss triggered by runoff is one of the most important sources of non-point pollution. The effects of grass hedges (Melilotus albus and Pennisetum alopecuroides) on atrazine runoff under different rain intensities and slope gradients were evaluated. The plot-scale experiments were carried out on a maize (Zea mays) field on slopes with 15% and 20% gradients using simulated rainfall (rain intensity of 30 and 45 mm h−1). Atrazine residues were investigated in runoff water and soil taken from three depths (0–5, 5–10, and 10–15 cm) in the middle and base of the slope after runoff events. Total atrazine loss in runoff water ranged from 2.3% to 4.9% of that applied from plots without grass hedges. Grass hedges decreased atrazine loss by 37%-76% and surface runoff by 27%-72%, and Pennisetum showed better efficacy than Melilotus, especially under higher rain intensity. Atrazine loss showed a significant positive linear correlation with surface runoff volume. Grass hedges had a more significant effect on atrazine loss than rain intensity and slope gradient. But they functioned less effectively if used under intense rain or/and steep slope conditions. Atrazine residues remained in the surface 15 cm soil were higher for the plots with grass hedges than the control plots. These results suggest that grass hedges not only significantly reduced atrazine loss by reducing the surface runoff, but also reduced the amount of atrazine leaching to deeper soil layer. P. alopecuroides was a suitable grass-hedge species for controlling atrazine losses in northern China and similar regions. Other management practices or control measures should be integrated with grass hedges in strongly sloping cropland in high-rainfall areas to maintain pesticide losses at an acceptable level.

The emergent plants Acorus calamus, Lythrum salicaria, and Scirpus tabernaemontani were exposed to atrazine for 15, 30, 45, and 60 days in a hydroponic system. Effects were evaluated investigating plant growth, chlorophyll (Chl) content, peroxidase (POD) activity, and malondialdehyde (MDA) content. Results showed that selected plants survived in culture solution with atrazine ≤8 mg L(-1), but relative growth rates decreased significantly in the first 15-day exposure. Chla content decreased, but MDA increased with increasing atrazine concentration. S. tabernaemontani was the most insensitive species, followed by A. calamus and L.salicaria. The growth indicators exhibited significant changes in the early stage of atrazine exposure; subsequently, the negative impacts weakened and disappeared. Plant growth may be more representative of emergent plant fitness than physiological endpoints in toxicity assessment of herbicides to emergent plants.

Atrazine is frequently detected in surface runoff and poses a potential threat to the environment. Grass hedges may minimize runoff loss of atrazine from crop fields. Therefore, the effectiveness of two grass hedges (Melilotus albus and Pennisetum alopecuroides) in controlling atrazine runoff was investigated using simulated rainfall on lands at different slope gradients (15 and 20%) in northern China. Results showed that a storm (40 mm in 1 h), occurring 4 h after atrazine application, caused a loss of 3% of the applied amount. Atrazine loss under 20% slope was significantly greater than that under 15% slope in control plots. Atrazine exports associated with the water fraction accounted for the majority of total loss. Pennisetum hedges were more efficient in controlling atrazine loss with runoff compared to Melilotus hedges. No significant difference in the capacity of grass hedges to reduce atrazine exports was observed between 15 and 20% slopes. These findings suggest grass hedges are effective in minimizing atrazine runoff in northern China, and Pennisetum hedges should be preferentially used on sloping croplands in similar climatic regions.

The emergent hydrophyte Iris pseudacorus was constantly exposed over a 35-day period to atrazine in the laboratory. It could survive at an atrazine level up to 32 mg/L. Its relative growth rates were inhibited significantly when exposure dosage reached at or exceeded 2 mg/L (p < 0.05). No observed effect concentration and lowest observed effect concentration for growth were 1 and 2 mg/L, respectively. Chlorophyll a and b contents of the plant in all treatment groups were affected significantly, and chlorophyll a/b ratios of all atrazine treatment levels were pronouncedly higher than those of the control within 5 days of exposure (p < 0.05), but thereafter recovered to the level of the control. Differences of photosynthetic efficiency were significant between all atrazine treatments and the control; except for 1 mg/L on day 1 and 5, and 2 mg/L on day 1. I. pseudacorus did not show phytotoxicity symptoms after 35 days exposure to atrazine below 2 mg/L level, but photosynthetic efficiency had begun to decline.

For understanding the influence of initial concentrations of pesticides in the water body on removal efficiency of the contaminant by aquatic plants, one hydroponics experiment was used to investigate the influence of initial concentration (1–16 mg L−1) on toxicity and chlorpyrifos removal potential of Iris pseudacorus for 20 days under greenhouse conditions. An increased sensitivity to and reduced removal rate for chlorpyrifos were observed with increasing chlorpyrifos concentration. The relative growth rate (RGR) of I. pseudacorus was significantly inhibited in the presence of 4, 8 and 16 mg L−1 chlorpyrifos, and a negative relationship was also found between RGR and initial pesticide concentration. The half-life of chlorpyrifos was shortened in the hydroponic system with plants, indicating that I. pseudacorus accelerated chlorpyrifos removal from water. But the contribution of the plant to chlorpyrifos removal in the hydroponic phytoremediation system decreased with the increase of initial concentration of chlorpyrifos. The results also indicated that I. pseudacorus can efficiently eliminate chlorpyrifos and may ultimately serve as phytoremediation agents in the natural water body.

The potential of Acorus calamus to remove chlorpyrifos from water was assessed under laboratory conditions. Toxic effects of the insecticide in A. calamus were evaluated using pulse-amplitude modulated chlorophyll fluorescence techniques as well. At exposure concentrations above 8 mg L(-1), A. calamus showed obvious phytotoxic symptom with significant reduction in quantum efficiency of PSII (ΦPSII) and photochemical quenching coefficient (qP) in 20-day test; the inhibition of maximal quantum efficiency of PSII (Fv/Fm) was accompanied by a significant rise in initial chlorophyll fluorescence (Fo) within 15-day exposures. Fv/Fm and Fo recover to the normal level after 20-day exposure. The reduced removal rate to chlorpyrifos was observed with increase of initial chlorpyrifos concentrations. At application levels of 1, 2, and 4 mg L(-1), the disappearance rate of chlorpyrifos in the hydroponic system with plants was significantly greater than that without plants during the 20-day test periods. Chlorpyrifos was taken up from medium and transferred to above ground tissues by the plant and significant amounts of chlorpyrifos accumulated in plant tissues. The result indicated that A. calamus can promote the disappearance of chlorpyrifos from water and may be used for phytoremediation of water contaminated with a relatively low concentration of chlorpyrifos insecticide (