Agrichemical Applications Research Articles

Integrated application of grafted ZnO and fungicide to control the fungicide-resistant Colletotrichum spp

BackgroundThe Food and Agriculture Organization has reported approximately 40 % of food loss due to damage from plant pests and diseases, including fungal infections. Continuous application of agrichemicals for controlling fungal infection cause the occurrence of fungicide resistance. Colletotrichum spp., major causal agents for strawberry anthracnose, have gained concern for fungicide resistance issues. MethodsWe developed novel antifungal strategies in the present study by integrating multibranched flower-like ZnO (fZnO) and agrochemicals (trifloxystrobin). fZnO compounds were synthesised using an eco-friendly and efficient hydrothermal method. Charged polymers with steric structures, such as hydrophilic polyacrylic acid (PAA) and polyethyleneimine (PEI), were grafted onto fZnO surfaces to improve the suspension ability of the compounds. We used the grafted fZnO compounds in combination with the fungicide trifloxystrobin to evaluate the in vitro and in vivo activities. Significant findingsGrafted fZnO (80 ppm) and trifloxystrobin (100 ppm) effectively inhibited the growth of fungicide-resistant Colletotrichum spp. and limited strawberry anthracnose on leaves. PEI-grafted fZnO shows promise as an eco-friendly additive in sustainable agriculture due to its photocatalytic activity and ability to withstand environmental factors.

Recent Advances in Bio-management of Plant Diseases

Constantly increasing global human populations has put agricultural sector under astounding pressure to fulfil food demands growing worldwide. In order to optimize crop production, usage of agrochemicals in intensive agronomic practices have increased alarmingly. The negative impact of excessive application of agrichemicals on food production, human health and environment raises concerns about its long-term field application. Exploration of alternative means of crop protection and optimization, therefore, warrants inexpensive and environmentally friendly strategy. Use of microbes or microbes-based products among many options is one such important strategy that provides solution to the problems. In this regard, many biocontrol measures have been practiced over time, and some of them have shown exceptional potential and success. Realizing the importance of soil microbiota in crop optimization while reducing the chemical inputs, significance of plant beneficial bacteria in the amelioration of biotic stresses especially the phytopathogens employing microbiome management, microbial volatilomes, and nano-bioformulations is discussed. The relationship between the agriculturally useful soil microbiomes and food crops enables the development of microbes-based antagonist strategies for low-cost production of food crops in worrying open field environment.

Photosynthesis Responses of Tibetan Freshwater Algae Chlorella vulgaris to Herbicide Glyphosate.

With the development of agriculture and the widespread application of agrichemicals in Tibet, herbicide residues have become a threat to the ecological safety of Tibetan water bodies. Algae, as the producers in the food chain in water bodies, play an important role in aquatic ecosystems. Therefore, the impact of herbicides on Tibetan algae is of great significance for evaluating ecological health and the protection of Tibetan water ecosystems. In this study, we investigated the inhibitory effect of glyphosate, a herbicide, on the photosynthetic system of Chlorella vulgaris, Tibetan algae, by determining chlorophyll fluorescence and the activity of an antioxidant system. The results revealed that glyphosate at low concentration did not affect the photosynthetic activity of C. vulgaris; however, glyphosate at a high concentration significantly inhibited photosynthetic activity and reduced pigment content. Moreover, high levels of glyphosate also decreased photochemical efficiency and electron transport rate and resulted in ROS accumulation, high SOD activity, and lipid peroxidation. These results suggested that glyphosate could decrease the primary production of aquatic ecosystems and influence their performance. Therefore, reducing the herbicide levels could protect the Tibetan aquatic environment and maintain the health of ecosystems.

A Case Study: Arsenic, Cadmium and Copper Distribution in the Soil–Rice System in Two Main Rice-Producing Provinces in China

Arsenic (As) and cadmium (Cd) pose great risk to rice plants and human health. Copper (Cu) agrichemicals also draw increasing attention. This study investigated the distributions of As, Cd and Cu in the soil–rice system in two major rice-producing provinces, Hunan and Jiangxi, China. Arsenic in soils at site A in Hunan reached 47.95–60.25 mg/kg, all exceeding the national standard (GB15618-2018), but As in rice was all below the safe limit for humans (0.20 mg/kg, GB2762-2017). In contrast, As in all rice husks and 5% of grain samples from Jiangxi exceeded the safe limit, while As in soils was 3.40–9.92 mg/kg, all below the standard. Cadmium in soils at site A and site B in Hunan were 3.96–5.11 and 1.83–2.77 mg/kg, respectively, all exceeding the national standard; Cd in 60% of rice grains exceeded the safe limit (0.20 mg/kg, GB2762-2017). Despite Cd in soils from Jiangxi being much lower (0.20–0.34 mg/kg), Cd in 56% of the rice grains exceeded the safe limit. The different distribution patterns of As and Cd in the soil–rice system probably result from the dynamic environmental conditions during farming practice. Risk from dietary products made from rice husks should also be considered. Although not regulated in rice, Cu in the soil from Hunan exceeds the national standard. This study helps to understand As and Cd pollution in paddies and its risk to human health, and suggests limiting the application of Cu-based agrichemicals.

Advances in the green synthesis and agrichemical applications of oxathiapiprolin derivatives.

Oxathiapiprolin was developed with high antifungal activity and novel target protein and is used in the oomycetes control for crop protection. The structural modifications of oxathiapiprolin are summarized. The achievements and challenges in the structural modification of oxathiapiprolin are also discussed in this mini review. The outlook in this field is perspected according to our own opinion and understanding on the development of oxysterol binding protein inhibition fungicides.

Foliar Application of Zn Agrichemicals Affects the Bioavailability of Arsenic, Cadmium and Micronutrients to Rice (Oryza sativa L.) in Flooded Paddy Soil

Zinc (Zn) is a key micronutrient affecting bio-functions of crops. Impacts of foliar application of three forms of Zn-containing agrichemicals on the physiology of rice seedlings and their uptake of heavy metal(loid)s and micronutrients from fully flooded paddy soils were investigated in a greenhouse study. Rice seedlings 45 days after germination were randomly exposed to an equivalent amount of 100 mg L−1 of zinc oxide nanoparticles (ZnONPs), zinc oxide bulk particles (ZnOBPs), and zinc salts (Zn2+) through foliar exposure. At termination, rice seedlings were divided into roots and shoots and the concerned metal contents in plant tissues were determined with an inductively coupled plasma mass spectrometry (ICP-MS). Our results demonstrated that all Zn agrichemicals displayed a similar effect on plant growth, but ZnONPs led to the greatest root exudate excretion and greatest inhibition in arsenic (As) uptake. Foliar application of ZnONPs resulted in 28% less As in rice shoots while Zn2+ only caused a 15% decrease in As accumulation in the same tissues. ZnOBPs had minimal impact on As concentration in rice shoots. ZnONPs also promoted iron (Fe) and copper (Cu) uptake in rice shoots, both of which are essential micronutrients for humans. The results suggest that foliar application of ZnONPs resulted in more favorable outcomes for plant growth and food safety than other two types of Zn. Overall, our results showed that application of nanoagrichemicals have important food safety and nutrition implications in addition to their agronomical roles and ZnONPs could be potentially used to alleviate As uptake and fortify Zn and other essential micronutrients in rice grains.

Emerging Technologies for Monitoring Plant Health in Vivo.

In the coming decades, increasing agricultural productivity is all-important. As the global population is growing rapidly and putting increased demand on food supply, poor soil quality, drought, flooding, increasing temperatures, and novel plant diseases are negatively impacting yields worldwide. One method to increase yields is plant health monitoring and rapid detection of disease, nutrient deficiencies, or drought. Monitoring plant health will allow for precise application of agrichemicals, fertilizers, and water in order to maximize yields. In vivo plant sensors are an emerging technology with the potential to increase agricultural productivity. In this mini-review, we discuss three major approaches of in vivo sensors for plant health monitoring, including genetic engineering, imaging and spectroscopy, and electrical.

ThThnated Development of a pH assisted AgNP-based colorimetric sensor Array for simultaneous identification of phosalone and azinphosmethyl pesticides.

Development of simple and rapid methods for identification of pesticides, due to their broad usage and harmful effects on mammals, has been known as a critical demand. Herein, we have introduced a silver nanoparticle (AgNP) based colorimetric sensor array for simultaneous identification of Azinphosmethyl (AM) and Phosalone (PS) pesticides. In the presence of the target pesticides, unmodified AgNPs at various pHs (4.5, 5.5 and 9.5) showed different aggregation behaviors. As a result of aggregation, the color and UV-Vis spectra of AgNPs changed differentially, leading to distinct response patterns for AM and PS. The aggregation induced spectral changes of AgNPs, were used to identify AM and PS with the help of linear discriminant analysis (LDA). The applicability of the proposed sensor array was then evaluated by identifying the target pesticides in apple samples. Altogether, the developed AgNPs based colorimetric sensor array can be potentially exploited as an efficient discrimination tool in the near future for agrichemical applications.

Epidemiology of Exobasidium Leaf and Fruit Spot of Rabbiteye Blueberry: Pathogen Overwintering, Primary Infection, and Disease Progression on Leaves and Fruit.

Epidemiological field studies utilizing disease monitoring, spore trapping, and trap plants were conducted on rabbiteye blueberry (Vaccinium virgatum) between 2014 and 2017 to shed light on the epidemiology of Exobasidium leaf and fruit spot, an emerging disease in the southeastern United States caused by the fungus Exobasidium maculosum. Wash plating of field-collected blueberry tissue from the late dormant season through bud expansion showed that the pathogen overwintered epiphytically on blueberry plants in the field, most likely in its yeast-like conidial stage. Agrichemical applications during the dormant season altered epiphytic populations of the pathogen, which correlated directly with leaf spot incidence later in the spring. Disease monitoring of field plants and weekly exposure of potted trap plants revealed that young leaves at the mouse-ear stage were most susceptible to infection, that disease incidence on leaves progressed monocyclically, and that infection periods were associated with rainfall variables such as the number of days per week with ≥1.0 mm of rain or cumulative weekly rainfall. Weekly spore trapping with an Andersen sampler showed that airborne inoculum was detected only after sporulating leaf lesions producing basidiospores were present in the field, suggesting that the primary inoculum is not airborne. The first symptoms on young, green fruit were observed soon after petal fall (requiring removal of the waxy fruit layer to visualize lesions), and visible disease progress on fruit was delayed by 1 to 3 weeks relative to that on leaves. Fruit infection of field plants and trap plants occurred before airborne propagules were detected by spore trapping and before sporulating leaf lesions were present in the field. Hence, this study showed that fruit infections are initiated by the same initial inoculum as leaf infections but it was not possible to conclusively exclude the possibility of a contribution of basidiospore inoculum from leaf lesions to disease progress on later developing fruit. This is one of only a few studies addressing the epidemiology and disease cycle of an Exobasidium sp. in a pathosystem where artificial inoculation has not been possible to date.

Spray Application Efficiency from a Multi-Rotor Unmanned Aerial Vehicle Configured for Aerial Pesticide Application

HighlightsThe swath pattern was measured from an Agras MG-1 UAV spraying fine and extra-coarse droplet spectra.The recommended lane separation of 3.6 m did not differ for the two droplet size classes tested in this study.The applied spray deposited within the swath was higher with extra-coarse (>90%) than with fine (73%) droplets.There was potential for substantial downwind drift with fine droplets, even when flying close to the ground at low speed.Abstract. While there is increasing interest in the use of small, multi-rotor UAVs for application of agrichemicals, there is also uncertainty about their performance. Consequently, the purpose of this study was to quantify the performance of an Agras MG-1 with modified nozzle positions that, at the time of writing, was being used for commercial spraying in New Zealand. The approach was to release spray from the UAV along a single 50 m line. Spray deposits were measured using horizontal collectors placed on the ground in three 15 m transects centered on, and perpendicular to, the flight line. Airborne deposits were measured with a 10 m mast that supported spherical samplers at 1 m vertical intervals. Analysis of deposition data was undertaken to quantify factors influencing overall swath pattern variability, lane separation associated with a coefficient of variation (CV) of deposition of 30%, and spray application efficiency, which is the proportion of applied spray deposited within the swath. For two droplet size classes (extra-coarse and fine), the lane separation associated with a CV of 30% was about 3.6 m, with no significant effect of droplet size. This is a surprising result and may reflect the relatively small range of environmental conditions experienced during the field tests, including wind speed, which was relatively low for all tests. We speculate that this result may also be a consequence of the strong downwash. The swath width was positively correlated with wind speed. Spray efficiency was shown to be high (>90%) for the extra-coarse droplets but dropped significantly (73%) with the fine droplet spectrum. Combining in-swath deposition with the amount of airborne spray sampled in a 10 m vertical profile close to the edge of the swath accounted for 98.0% of the spray released with the extra-coarse spectrum but only 88.6% of the spray with the fine droplet spectrum. These results highlight that even with UAVs flying relatively close to the ground at a low forward speed, there is potential for substantial drift downwind of the swath when using smaller droplet size classes. Overall, the swath pattern was reasonably consistent across the two droplet size classes and for the narrow range of operational and meteorological conditions tested. Keywords: Aerial spraying, Pesticides, Spray application efficiency, Spray deposition, Swath pattern, UAV, Unmanned aerial vehicle.

Impact of kiwifruit bacterial canker on productivity of cv. Hayward kiwifruit using observational data and multivariable analysis

A virulent strain of Pseudomonas syringae pv. actinidiae biovar 3 (Psa), which causes bacterial canker in kiwifruit, was first recorded in New Zealand in November 2010. This strain has severely affected Actinidia chinensis var. chinensis ‘Hort16A’ kiwifruit productivity but its effect on green Actinidia chinensis var. deliciosa ‘Hayward’ kiwifruit productivity has been variable. An observational study design was used to develop explanatory models to quantify the impacts of Psa infection on productivity (tray equivalents per hectare) of Hayward kiwifruit harvested in 2012, using data captured by industry from 2599 orchards. A total of 934 orchards were Psa positive at the end of the study period. Multivariable linear regression was used to model 2012 productivity in the presence of Psa, while controlling for regional differences, elevation, 2011 productivity, harvest dates and application of agrichemicals. The model showed productivity was initially higher in the presence of Psa, and was not reduced until after 1 year of infection. The relationship between protective spray use and productivity was also quantified. It is likely that improved disease management has offset the impact of the disease and future research should consider a reassessment of the effects of disease after longer term exposure to Psa in New Zealand. The use of an observational cohort study to assess disease impacts using multivariable analysis could have wider application in the field of plant epidemiology.

Learning in and about rural places: Connections and tensions between students’ everyday experiences and environmental quality issues in their community

Guided by sociocultural perspectives on the importance of place as a resource for learning, we investigated 14- and 15-year old students’ understandings of their community and water quality during a school-based watershed unit. Methods included a theory-driven thematic analysis of field notes and video transcripts from four biology classrooms, a qualitative and quantitative analysis of 67 pairs of matched pre- and post-intervention mindmaps, and a content analysis of 73 student reflections. As they learned about water quality, learners recognized the relevance of the watershed’s health to the health of their community. Students acknowledged the impacts of local economically driven activities (e.g., natural gas wells, application of agrichemicals) and leisure activities (e.g., boating, fishing) on the watershed’s environmental health. As students learned in and about their watershed, they experienced both connections and tensions between their everyday experiences and the environmental problems in their community. The students suggested individual sustainability actions needed to address water quality issues; however, the students struggled to understand how to act collectively. Implications of rural experiences as assets to future environmental sciences learning are discussed as well as the implications of educational experiences that do not include an advocacy component when students uncover environmental health issues. We suggest further consideration is needed on how to help young people develop action-oriented science knowledge, not just inert knowledge of environmental problems, during place-based education units.

Fate and transport modeling of phthalate esters from biosolid amended soil under corn cultivation

Phthalate esters (PAEs) are prevalent in the environment due to the broad range of industrial, agriculture and domestic applications. The ubiquitous use of PAEs has resulted in their potential to reach groundwater sources through application of agri-chemicals and municipal biosolids. A study was conducted to monitor the fate and transport of seven commonly detected PAEs in the environment including: dimethyl phthalate (DMP), diethyl phthalate (DEP), benzyl butyl phthalate (BBP), bis(di-ethyl hexyl) phthalate (DEHP), di-n-octyl phthalate (DnOP), dipentyl phthalate (DPP), and di-n-butyl phthalate (DnBP). Biosolids sourced from the Halifax Regional Municipality were applied at three rates on field-based lysimeter cells which were cropped to corn (Zea mays) for one growing season. In the present study, breakthrough curves (BTCs) were established for phthalates leaching from a corn-cultivated agricultural soil profile. The HYDRUS-1D model and a two-site sorption model were applied to predict transport parameters of PAEs using an inverse solution approach. Results of our research revealed that higher PAE adsorption was observed based on increasing carbon chain number. In addition, higher values of F (i.e. the fraction of type-1 sorption sites assumed to be in equilibrium with the solution phase) and lower values of D (i.e. dispersion coefficient) were observed for PAEs with large carbon chains which was validated both through the empirical dataset and the model simulations.

Spray retention on whole plants: modelling, simulations and experiments

Retention of sprays on plants is a critical component influencing the effectiveness of agrichemical applications. Previous simulations of spray retention by plants gave poor agreement for hard-to-wet species when compared with actual measured retention. A new model is developed here that accounts for: species wettability, impaction angle, droplet bounce, partial retention on shatter, a variable time to shatter, and the number of daughter droplets produced. The aim of this study was to compare predictions from the new model with data obtained by spraying five mixtures via five nozzles onto easy-to-wet cotton (Gossypium hirsutum L.), and hard-to-wet wheat (Triticum aestivum L.) and fat hen (Chenopodium album L.). The new model correctly predicts retention to be highest on cotton and lowest on wheat. The trend in both measured data and the model predictions is for retention to decrease with increasing droplet size, on all three plant species. Formulation is correctly predicted to have little influence on retention by easy-to-wet cotton plants and to enhance retention by the harder-to-wet wheat and fat hen plants. The parameters that describe partial retention on shatter and variable time to shatter have a substantial influence on retention, as they affect primary or secondary droplet capture. A better understanding of the kinetic energy effects and the interactions between the formulation and the leaf surface are needed to refine their input values.

Solar UV-treatment of water samples for stripping-voltammetric determination of trace heavy metals in Awash river, Ethiopia.

We report about testing a new mobile and sustainable water sample digestion method in a preliminary field trial in Ethiopia. In order to determine heavy metals at the ultra-trace level by stripping voltammetric techniques in water samples from Awash River, we applied our new method of solar UV-assisted sample pretreatment to destroy the relevant interfering dissolved organic matter. The field tests revealed that 24 h of solar UV irradiation were sufficient to achieve the same sample pretreatment results as with classic digestion method based on intense and hard UV. Analytical results of this study suggest that both a hydroelectric power station and agrichemical applications at Koka Lake have increased the levels of the investigated metals zinc, cadmium, lead, copper, cobalt, nickel, and uranium.

Spatial distribution and source identification of heavy metals in soils under different land uses in a sewage irrigation region, northwest China

Heavy metal pollution is of major concern due to its potential threat to ecosystem safety and human health. To give a valuable insight into the status of heavy metal pollution in a sewage irrigation region in northwest China, this paper thoroughly studied the spatial distribution and possible source of heavy metals in soils under different land uses. Soil samples were collected from arable lands (maize field, orchard, and paddy field) and nonarable lands (village and barren hill) from a sewage irrigation region, northwest China. The concentrations of Cd, Cr, Cu, Mn, Ni, Pb, and Zn in the soils, together with soil pH, soil organic matter (SOM), and soil particle size distribution, were detected. GIS-based approach was employed to construct the spatial distribution maps of heavy metals, and multivariate analysis was used to identify their possible source. Although elevated concentrations of Zn, Pb, and Cu are detected, Cd is the priority pollutant in the soils. Land use, location, and SOM are crucial factors affecting metal distribution in the soils. Metal concentrations in different land uses arrange in the order of orchard > paddy field/maize field > village > barren hill. The area within the basin of Dongdagou stream presents the most pollution, whereas the northeast side far from the stream is the least. Irrigation water both from Dongdagou stream and the Yellow River are deemed as primary sources of Cd, Zn, Pb, and Cu. Besides, agrichemical application particularly contributes to metal accumulation in orchard soils, and Cd and Zn partially derive from atmospheric deposition. Nickel and Mn predominately originate from the soils. When studying metal pollution in soils, land use should be taken into account because of its important roles in determining metal concentrations. In the study area, arable lands are more likely to be polluted by Cd, Zn, Pb, and Cu than nonarable lands via sewage irrigation; moreover, agrichemical application and atmospheric deposition also should be held responsible for metal accumulation in the soils.

Natural parasitism of Romanomermis iyengari (Welch) (Nematoda: Mermithidae) on various species of mosquitoes breeding in rice fields in Pondicherry, India

Natural habitat of Romanomermis iyengari, an entomophilic mermithid nematode, is rice field. Parasitism of this nematode on mosquito larvae breeding in rice fields in Pondicherry, India, has been studied in 1979. The present study was to find out its persistence in the same habitat, after many years of agricultural practices. Evaluation of parasitism on mosquito larvae was carried out during two rice cultivation seasons at a schedule of 1week prior, and 1 and 2weeks after transplantation of paddy. Larval stages of mosquito species such as Culex tritaeniorhynchus, Culex vishnui, Anopheles vagus, and Anopheles subpictus showed parasitism of R. iyengari. Parasitism was the highest on C. tritaeniorhynchus with a maximum of 15.38% during season I and 17.85% during season II. Followed by this, it was on A. vagus (10.82% and 9.43%), C. vishnui (7.37% and 8.69%), and A. subpictus (3.70% and 6.36%). The overall density of mosquito larvae and level of parasitism of R. iyengari on them during season II was significantly higher than that of season I. The parasitism was maximum at 1week before transplantation and showed a decreasing trend towards 2weeks after transplantation, during both the seasons. The level of natural parasitism of R. iyengari during the present investigation was higher than that observed in the same ecosystem almost 35years ago. This is clearly an indication towards the capability of the nematode to withstand several years of agricultural practices, including pesticide and agrichemical application. Hence, if applied at sufficient level and frequency, this nematode could act as a successful biocontrol agent against mosquitoes breeding in rice fields.

Pesticide Use Practices in Rural Armenia

ABSTRACT Pesticide use can have adverse effects on both human health and the environment. Inappropriate use of pesticides increases the health risk to those who work with or live around pesticides. Educational programs for agricultural workers on the proper use of pesticides and personal protective equipment coupled with pesticide regulations are important tools to reduce the associated health risks. The authors conducted a survey (N = 2336) on pesticide use practices in the Ararat Valley of Armenia in 2000–2006. This study was a cross-sectional design. A multistage sampling method was implemented in the selection of the study population. The authors developed a questionnaire containing 173 questions to evaluate demographic characteristics, health conditions, and details of pesticides use practices. The intensity of pesticide use was high; 82.8% of respondents used them. More than 150 brand names of pesticides were in use. Unregistered, obsolete, expired, and banned compounds were found in active use. Poor compliance with the basic rules of pesticide safety was found throughout the study population, with 21.3% using gloves and only 11% using respirators. The agricultural workers’ knowledge of the toxic properties of these pesticides as well as basic hygienic norms was very low. In some instances, the number of agrichemical applications to crops, particularly cucumbers and melons, reached 40 applications during the growing season. Better protection and training of pesticide users in Armenia is needed.

Synchrotron Verification of TiO2 Accumulation in Cucumber Fruit: A Possible Pathway of TiO2 Nanoparticle Transfer from Soil into the Food Chain

The transfer of nanoparticles (NPs) into the food chain through edible plants is of great concern. Cucumis sativus L. is a freshly consumed garden vegetable that could be in contact with NPs through biosolids and direct agrichemical application. In this research, cucumber plants were cultivated for 150 days in sandy loam soil treated with 0 to 750 mg TiO2 NPs kg(-1). Fruits were analyzed using synchrotron μ-XRF and μ-XANES, ICP-OES, and biochemical assays. Results showed that catalase in leaves increased (U mg(-1) protein) from 58.8 in control to 78.8 in 750 mg kg(-1) treatment; while ascorbate peroxidase decreased from 21.9 to 14.1 in 500 mg kg(-1) treatment. Moreover, total chlorophyll content in leaves increased in the 750 mg kg(-1) treatment. Compared to control, FTIR spectra of fruit from TiO2 NP treated plants showed significant differences (p ≤ 0.05) in band areas of amide, lignin, and carbohydrates, suggesting macromolecule modification of cucumber fruit. In addition, compared with control, plants treated with 500 mg kg(-1) had 35% more potassium and 34% more phosphorus. For the first time, μ-XRF and μ-XANES showed root-to-fruit translocation of TiO2 in cucumber without biotransformation. This suggests TiO2 could be introduced into the food chain with unknown consequences.

Comparison of earthworm and chemical assays of the bioavailability of aged 1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethylene, 1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane, and heavy metals in orchard soils

Orchard soils can contain elevated concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT), and heavy metals as a result of historical agrichemical applications. The bioavailability of p,p'-DDE, p,p'-DDT, As, Cd, Cu, and Pb from five field-aged New Zealand orchards and three grazing soils was assessed by using a 28-d bioassay with Aporrectodea caliginosa and chemical assays. Significant relationships were found between total soil and earthworm tissue concentrations for p,p'-DDE (p < 0.001), p,p'-DDT (p < 0.001), Cu (p < 0.001), and Pb (p < 0.01). Two neutral salt solutions, 0.01 M CaCl(2) and 1 M NH(4)NO(3), were used as surrogate measures of the bioavailability of heavy metals. Copper was the only heavy metal for which significant correlations were found between neutral-salt-extractable and earthworm tissue concentrations (p < 0.001). Up to 28% of the aged DDT residues were released from the soils by Tenax over a 24-h extraction period. Significant relationships (p < 0.01) between the Tenax-extractable and earthworm tissue concentrations for p,p'-DDE and p,p'-DDT showed that Tenax provides a good surrogate measure of the bioavailability of these compounds to A. caliginosa. Surprisingly, there was a similarly significant relationship (p < 0.001) between the total soil and earthworm tissue concentrations for p,p'-DDE and p,p'-DDT, suggesting that total soil concentrations alone were sufficient to predict uptake by A. caliginosa. These results demonstrate that the aged agrichemical residues in orchard soils, and particularly p,p'-DDE and p,p'-DDT, remain highly bioavailable to A. caliginosa despite decades of weathering and continue to present an environmental risk.