Enzyme- and Relative Humidity-Responsive Antimicrobial Fibers for Active Food Packaging.

Active food packaging materials that are sustainable, biodegradable, and capable of precise delivery of antimicrobial active ingredients (AIs) are in high demand. Here, we report the development of novel enzyme- and relative humidity (RH)-responsive antimicrobial fibers with an average diameter of 225 ± 50 nm, which can be deposited as a functional layer for packaging materials. Cellulose nanocrystals (CNCs), zein (protein), and starch were electrospun to form multistimuli-responsive fibers that incorporated a cocktail of both free nature-derived antimicrobials such as thyme oil, citric acid, and nisin and cyclodextrin-inclusion complexes (CD-ICs) of thyme oil, sorbic acid, and nisin. The multistimuli-responsive fibers were designed to release the free AIs and CD-ICs of AIs in response to enzyme and RH triggers, respectively. Enzyme-responsive release of free AIs is achieved due to the degradation of selected polymers, forming the backbone of the fibers. For instance, protease enzyme can degrade zein polymer, further accelerating the release of AIs from the fibers. Similarly, RH-responsive release is obtained due to the unique chemical nature of CD-ICs, enabling the release of AIs from the cavity at high RH. The successful synthesis of CD-ICs of AIs and incorporation of antimicrobials in the structure of the multistimuli-responsive fibers were confirmed by X-ray diffraction and Fourier transform infrared spectrometry. Fibers were capable of releasing free AIs when triggered by microorganism-exudated enzymes in a dose-dependent manner and releasing CD-IC form of AIs in response to high relative humidity (95% RH). With 24 h of exposure, stimuli-responsive fibers significantly reduced the populations of foodborne pathogenic bacterial surrogates Escherichia coli (by ∼5 log unit) and Listeria innocua (by ∼5 log unit), as well as fungi Aspergillus fumigatus (by >1 log unit). More importantly, the fibers released more AIs at 95% RH than at 50% RH, which resulted in a higher population reduction of E. coli at 95% RH. Such biodegradable, nontoxic, and multistimuli-responsive antimicrobial fibers have great potential for broad applications as active and smart packaging systems.

Multilaboratory Collaborative Study of a Nontarget Data Acquisition for Target Analysis (nDATA) Workflow Using Liquid Chromatography-High-Resolution Accurate Mass Spectrometry for Pesticide Screening in Fruits and Vegetables.

Nontarget data acquisition for target analysis (nDATA) workflows using liquid chromatography-high-resolution accurate mass (LC-HRAM) spectrometry, spectral screening software, and a compound database have generated interest because of their potential for screening of pesticides in foods. However, these procedures and particularly the instrument processing software need to be thoroughly evaluated before implementation in routine analysis. In this work, 25 laboratories participated in a collaborative study to evaluate an nDATA workflow on high moisture produce (apple, banana, broccoli, carrot, grape, lettuce, orange, potato, strawberry, and tomato). Samples were extracted in each laboratory by quick, easy, cheap, effective, rugged, and safe (QuEChERS), and data were acquired by ultrahigh-performance liquid chromatography (UHPLC) coupled to a high-resolution quadrupole Orbitrap (QOrbitrap) or quadrupole time-of-flight (QTOF) mass spectrometer operating in full-scan mass spectrometry (MS) data-independent tandem mass spectrometry (LC-FS MS/DIA MS/MS) acquisition mode. The nDATA workflow was evaluated using a restricted compound database with 51 pesticides and vendor processing software. Pesticide identifications were determined by retention time (tR, ±0.5 min relative to the reference retention times used in the compound database) and mass errors (δM) of the precursor (RTP, δM ≤ ±5 ppm) and product ions (RTPI, δM ≤ ±10 ppm). The elution profiles of all 51 pesticides were within ±0.5 min among 24 of the participating laboratories. Successful screening was determined by false positive and false negative rates of <5% in unfortified (pesticide-free) and fortified (10 and 100 µg/kg) produce matrices. Pesticide responses were dependent on the pesticide, matrix, and instrument. The false negative rates were 0.7 and 0.1% at 10 and 100 µg/kg, respectively, and the false positive rate was 1.1% from results of the participating LC-HRAM platforms. Further evaluation was achieved by providing produce samples spiked with pesticides at concentrations blinded to the laboratories. Twenty-two of the 25 laboratories were successful in identifying all fortified pesticides (0-7 pesticides ranging from 5 to 50 µg/kg) for each produce sample (99.7% detection rate). These studies provide convincing evidence that the nDATA comprehensive approach broadens the screening capabilities of pesticide analyses and provide a platform with the potential to be easily extended to a larger number of other chemical residues and contaminants in foods.

Effects of the neonicotinoid acetamiprid in syrup on Bombus impatiens (Hymenoptera: Apidae) microcolony development.

Worldwide, many pollinator populations are in decline. Population reductions have been documented for the agriculturally important honey bee (Apis mellifera), and other bee species such as bumble bees that are also critical for pollinating crops and natural landscapes. A variety of factors contribute to the observed population reductions, including exposure to agrochemicals. In recent decades, neonicotinoid pesticide use has dramatically increased, as have concerns regarding the safety of these chemicals for pollinator health. Here we assessed the toxicity of the neonicotinoid acetamiprid to the bumble bee Bombus impatiens, a species commercially available for use in agricultural settings in North America. Using the microcolony model, we examined nest growth, development and subsequent nest productivity as measured by drone production. We found that high concentrations of acetamiprid in syrup (11,300 µg/L) significantly impacted nest growth and development, and ultimately drone production, and exposure to 1,130 µg/L acetamiprid also significantly decreased drone production. The no observable adverse effect level was 113 µg/L. Overall, acetamiprid delivered in syrup can negatively impact B. impatiens nest development and productivity, however only at concentrations above which would be expected in the environment when used according to label rates.

Tracking Pesticide Residues to a Plant Genus Using Palynology in Pollen Trapped from Honey Bees (Hymenoptera: Apidae) at Ornamental Plant Nurseries.

Worldwide studies have used the technique of pollen trapping, collecting pollen loads from returning honey bee (Apis mellifera L.) (Hymenoptera: Apidae) foragers, to evaluate the exposure of honey bees to pesticides through pollen and as a biomonitoring tool. Typically, these surveys have found frequent contamination of pollen with multiple pesticides, with most of the estimated risk of acute oral toxicity to honey bees coming from insecticides. In our survey of pesticides in trapped pollen from three commercial ornamental plant nurseries in Connecticut, we found most samples within the range of acute toxicity in a previous state pollen survey, but a few samples at one nursery with unusually high acute oral toxicity. Using visual sorting by color of the pollen pellets collected in two samples from this nursery, followed by pesticide analysis of the sorted pollen and palynology to identify the plant sources of the pollen with the greatest acute toxicity of pesticide residues, we were able to associate pollen from the plant genus Spiraea L. (Rosales: Rosaceae) with extraordinarily high concentrations of thiamethoxam and clothianidin, and also with high concentrations of acephate and its metabolite methamidophos. This study is the first to trace highly toxic pollen collected by honey bees to a single plant genus. This method of tracking high toxicity pollen samples back to potential source plants could identify additional high-risk combinations of pesticide application methods and timing, movement into pollen, and attractiveness to bees that would be difficult to identify through modeling each of the contributing factors.

Co-exposure to the food additives SiO2 (E551) or TiO2 (E171) and the pesticide boscalid increases cytotoxicity and bioavailability of the pesticide in a tri-culture small intestinal epithelium model: Potential health implications.

Many toxicity investigations have evaluated the potential health risks of ingested engineered nanomaterials (iENMs); however, few have addressed the potential combined effects of iENMs and other toxic compounds (e.g. pesticides) in food. To address this knowledge gap, we investigated the effects of two widely used, partly nanoscale, engineered particulate food additives, TiO2 (E171) and SiO2 (E551), on the cytotoxicity and cellular uptake and translocation of the pesticide boscalid. Fasting food model (phosphate buffer) containing iENM (1% w/w), boscalid (10 or 150 ppm), or both, was processed using a simulated in vitro oral-gastric-small intestinal digestion system. The resulting small intestinal digesta was applied to an in vitro tri-culture small intestinal epithelium model, and effects on cell layer integrity, viability, cytotoxicity and production of reactive oxygen species (ROS) were assessed. Boscalid uptake and translocation was also quantified by LC/MS. Cytotoxicity and ROS production in cells exposed to combined iENM and boscalid were greater than in cells exposed to either iENM or boscalid alone. More importantly, translocation of boscalid across the tri-culture cellular layer was increased by 20% and 30% in the presence of TiO2 and SiO2, respectively. One possible mechanism for this increase is diminished epithelial cell health, as indicated by the elevated oxidative stress and cytotoxicity observed in co-exposed cells. In addition, analysis of boscalid in digesta supernatants revealed 16% and 30% more boscalid in supernatants from samples containing TiO2 and SiO2, respectively, suggesting that displacement of boscalid from flocculated digestive proteins by iENMs may also contribute to the increased translocation.

Exposure of Honey Bee (Apis mellifera L.) Colonies to Pesticides in Pollen, A Statewide Assessment in Maine.

In 2015, we conducted a statewide assessment of honey bee exposure to pesticides with assistance of volunteer beekeepers. Pollen trapping was conducted at 32 sites in the spring, summer, and early fall. Apiary locations ranged from unmanaged natural landscapes to managed agricultural or urban landscapes. Pollen samples at each site were aggregated over the collection dates and chemical residue analysis was conducted on each pollen sample for 190 pesticides and metabolites using HPLC/MS. Twenty-five different residues were detected for an average of 2.9 detections per site. Detections were dominated by fungicides, but risk, calculated as: ppb residue concentration/LD50, was mostly due to insecticides. Beekeeper perceived land-use in the vicinity of each apiary was associated with significant differences in the number of detections and residue concentrations, agricultural landscapes greater than nonagricultural. However, there was no significant difference in oral or contact risk quotients due to land-use type. The landscape composition surrounding apiaries, derived with GIS, determined pesticide exposure for honey bees when total detections, log pesticide residue concentration, and log contact risk quotients were used as measures. Partial least squares explained 43.9% of the variance in pesticide exposure due to landscape composition. The best predictors describing pesticide exposure were: area (ha) of blueberry, coniferous forest, and urban/developed land cover types. Maine is the most forested state in the United States (as determined by % land area forested, 93%) and a negative exponential decay was observed between land area in conifer forest and the number of pesticide detections per apiary.

Correction: Using a Hazard Quotient to Evaluate Pesticide Residues Detected in Pollen Trapped from Honey Bees (Apis mellifera) in Connecticut.

[This corrects the article DOI: 10.1371/journal.pone.0077550.].

Interlaboratory comparison of a general method to screen foods for pesticides using QuEChERs extraction with high performance liquid chromatography and high resolution mass spectrometry.

An interlaboratory comparison of a multipesticide residue analytical method is reported. The goal of the comparison was to evaluate the potential for liquid chromatography/high resolution mass spectrometry along with a specific automated screening procedure to allow the determination of the presence or absence of a set of targeted compounds without additional manual review. The method utilized an off the shelf QuEChERs based extraction followed by analysis with an orbitrap mass spectrometer with the data evaluated by ToxID. The method was tested at three laboratories, with three produce matrices (spinach, carrots, and oranges), and three levels of spiked pesticides with all analyses in triplicate. A series of 247 compounds were tested, and it was found that the three laboratories produced consistent data; however, manual review was still necessary. The data was shown to have no false negatives for 211 compounds in the three produce matrixes at 200 ppb. Of these 211 compounds, 189 had no false negatives at 50 ppb, and 129 had no false negatives at 10 ppb. The HRMS method was shown to be robust with similar data being achieved by all three laboratories and detectable concentrations only slightly above the range shown for triple quadrupole MS/MS.

Using a hazard quotient to evaluate pesticide residues detected in pollen trapped from honey bees (Apis mellifera) in Connecticut.

Analysis of pollen trapped from honey bees as they return to their hives provides a method of monitoring fluctuations in one route of pesticide exposure over location and time. We collected pollen from apiaries in five locations in Connecticut, including urban, rural, and mixed agricultural sites, for periods from two to five years. Pollen was analyzed for pesticide residues using a standard extraction method widely used for pesticides (QuEChERS) and liquid chromatography/mass spectrometric analysis. Sixty pesticides or metabolites were detected. Because the dose lethal to 50% of adult worker honey bees (LD50) is the only toxicity parameter available for a wide range of pesticides, and among our pesticides there were contact LD50 values ranging from 0.006 to >1000 µg per bee (range 166,000X), and even among insecticides LD50 values ranged from 0.006 to 59.8 µg/bee (10,000X); therefore we propose that in studies of honey bee exposure to pesticides that concentrations be reported as Hazard Quotients as well as in standard concentrations such as parts per billion. We used both contact and oral LD50 values to calculate Pollen Hazard Quotients (PHQ = concentration in ppb ÷ LD50 as µg/bee) when both were available. In this study, pesticide Pollen Hazard Quotients ranged from over 75,000 to 0.01. The pesticides with the greatest Pollen Hazard Quotients at the maximum concentrations found in our study were (in descending order): phosmet, Imidacloprid, indoxacarb, chlorpyrifos, fipronil, thiamethoxam, azinphos-methyl, and fenthion, all with at least one Pollen Hazard Quotient (using contact or oral LD50) over 500. At the maximum rate of pollen consumption by nurse bees, a Pollen Hazard Quotient of 500 would be approximately equivalent to consuming 0.5% of the LD50 per day. We also present an example of a Nectar Hazard Quotient and the percentage of LD50 per day at the maximum nectar consumption rate.

Movement of soil-applied imidacloprid and thiamethoxam into nectar and pollen of squash (Cucurbita pepo).

There has been recent interest in the threat to bees posed by the use of systemic insecticides. One concern is that systemic insecticides may translocate from the soil into pollen and nectar of plants, where they would be ingested by pollinators. This paper reports on the movement of two such systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, into the pollen and nectar of flowers of squash (Cucurbita pepo cultivars "Multipik," "Sunray" and "Bush Delicata") when applied to soil by two methods: (1) sprayed into soil before seeding, or (2) applied through drip irrigation in a single treatment after transplant. All insecticide treatments were within labeled rates for these compounds. Pollen and nectar samples were analyzed using a standard extraction method widely used for pesticides (QuEChERS) and liquid chromatography mass spectrometric analysis. The concentrations found in nectar, 10 ± 3 ppb (mean ± s.d) for imidacloprid and 11 ± 6 ppb for thiamethoxam, are higher than concentrations of neonicotinoid insecticides in nectar of canola and sunflower grown from treated seed, and similar to those found in a recent study of neonicotinoids applied to pumpkins at transplant and through drip irrigation. The concentrations in pollen, 14 ± 8 ppb for imidacloprid and 12 ± 9 ppb for thiamethoxam, are higher than those found for seed treatments in most studies, but at the low end of the range found in the pumpkin study. Our concentrations fall into the range being investigated for sublethal effects on honey bees and bumble bees.

Multiple routes of pesticide exposure for honey bees living near agricultural fields.

Populations of honey bees and other pollinators have declined worldwide in recent years. A variety of stressors have been implicated as potential causes, including agricultural pesticides. Neonicotinoid insecticides, which are widely used and highly toxic to honey bees, have been found in previous analyses of honey bee pollen and comb material. However, the routes of exposure have remained largely undefined. We used LC/MS-MS to analyze samples of honey bees, pollen stored in the hive and several potential exposure routes associated with plantings of neonicotinoid treated maize. Our results demonstrate that bees are exposed to these compounds and several other agricultural pesticides in several ways throughout the foraging period. During spring, extremely high levels of clothianidin and thiamethoxam were found in planter exhaust material produced during the planting of treated maize seed. We also found neonicotinoids in the soil of each field we sampled, including unplanted fields. Plants visited by foraging bees (dandelions) growing near these fields were found to contain neonicotinoids as well. This indicates deposition of neonicotinoids on the flowers, uptake by the root system, or both. Dead bees collected near hive entrances during the spring sampling period were found to contain clothianidin as well, although whether exposure was oral (consuming pollen) or by contact (soil/planter dust) is unclear. We also detected the insecticide clothianidin in pollen collected by bees and stored in the hive. When maize plants in our field reached anthesis, maize pollen from treated seed was found to contain clothianidin and other pesticides; and honey bees in our study readily collected maize pollen. These findings clarify some of the mechanisms by which honey bees may be exposed to agricultural pesticides throughout the growing season. These results have implications for a wide range of large-scale annual cropping systems that utilize neonicotinoid seed treatments.

Modeling the difference among Cucurbita in uptake and translocation of p,p'-dichlorophenyl-1,1-dichloroethylene.

Uptake of organic chemicals into plants depends on the properties of the contaminant and the physiology of the plant. A mass balance model based on fugacity was developed to quantify the uptake and transport in plants of a very hydrophobic chemical, p,p'-dichlorophenyl-1,1-dichloroethylene (DDE). The model included processes for sorption or influx of chemical with water from hydroponic solution to root and sorption or exchange of chemical between the shoot and air. Movement among compartments of the plant was governed by the transfer of water in xylem and phloem. The movement of water was entirely determined by transpiration, growth rate, and weight distribution among tissues. This model was used to predict the kinetics of uptake and movement of DDE from hydroponic solution by seedlings of two species of Cucurbitacea, cucumber and zucchini. These predictions were compared to the results of experiments in a companion paper. These experiments showed that the translocation of DDE in zucchini was much greater than in cucumber. The model correctly predicted the negligible uptake into the shoot of cucumber. The model predicted the greater uptake of DDE by zucchini only if the apparent partitioning of DDE in the xylem was 25-fold higher than that expected in pure water. Predictions using similar parameters were made for uptake and distribution of DDE for plants grown into fruit production in field soil contaminated with DDE. To match the observed concentration of DDE in fruit, the model coefficient for partitioning of DDE into water in phloem had to be increased to 200 times that in pure water.

Uptake and translocation of p,p'-dichlorodiphenyldichloroethylene supplied in hydroponics solution to Cucurbita.

Field studies show shoots of zucchini (Cucurbita pepo L.) accumulate various hydrophobic contaminants from soil, although many other plants do not, including cucumber (Cucumis sativus L.). To investigate the mechanism for this uptake, we presented p,p'-dichlorodiphenyldichloroethylene (DDE) to these two species in hydroponics solution. A mixture of DDE bound to Tenax beads stirred with a solution of water passing through a reservoir provided a flowing solution containing DDE at approximately 2 microg/L for many weeks duration. Approximately 90% of the DDE supplied in solution was adsorbed on the roots of both cucumber and zucchini. Less than 10% of the sorbed DDE was released subsequently when clean solution flowed past these contaminated roots for 9 d. The shoots of both species accumulated DDE, but the fraction that moved from the roots to the shoot in zucchini, ranging from 6 to 27% in various trials, was 10-fold greater than that in cucumber, 0.7 to 2%. The gradient in DDE concentration in zucchini tissues was in the order root more more than stem > petiole > leaf blade, indicating the movement was through the xylem in the transpiration stream. Some DDE in leaf blades might have been absorbed from the air, because the concentration in this tissue varied less with time, position in trough, or species, than did DDE in stems and petioles. The remarkable ability of zucchini to translocate DDE could not be attributed to differences in tissue composition, growth rate, distribution of weight among plant parts, or in the leaf area and rate of transpiration of water from leaves. Some other factor enables efficient translocation of hydrophobic organic contaminants in the xylem of zucchini.

Effect of mycorrhizal fungi on the phytoextraction of weathered p,p-DDE by Cucurbita pepo.

Field experiments were conducted to assess the impact of inoculation with mycorrhizal fungi on the accumulation of weathered p,p'-DDE from soil by three cultivars of zucchini (Cucurbita pepo spp. pepo cv Costata Romanesco, Goldrush, Raven). Three commercially available mycorrhizal products (BioVam, Myco-Vam, INVAM) were inoculated into the root system of the zucchini seedlings at planting. In agreement with our previous findings, plants not inoculated with fungi accumulated large but variable amounts of contaminant, with root bioconcentration factors (BCFs, ratio of p,p'-DDE, on a dry weight basis, in the root to that in the soil) ranging from 10 to 48 and stem BCFs ranging from 5.5 to 11. The total amount of contaminant phytoextracted during the 62 day growing season ranged from 0.72-2.9%. The effect of fungal inoculation on the release of weathered p,p'-DDE from soil and on the subsequent uptake of the parent compound by zucchini appeared to vary at the cultivar level. For Goldrush, fungal inoculation generally decreased tissue BCFs but because of slightly larger biomass, did not significantly impact the percent contaminant phytoextracted. Alternatively, for Costata, BioVam and Myco-Vam generally enhanced p,p'-DDE accumulation from soil, and increased the amount of contaminant phytoextracted by up to 34%. For Raven, BioVam reduced contaminant uptake whereas Myco-Vam and INVAM increased contaminant phytoextraction by 53 and 60%, respectively. The data show that fungal inoculation may significantly increase the remedial potential of C. pepo ssp. pepo. The apparent cultivar specific response to mycorrhizal inoculation is unexpected and the subject of ongoing investigation.

Soil amendments, plant age, and intercropping impact p,p'-DDE bioavailability to Cucurbita pepo.

Field experiments were conducted to optimize the phytoextraction of weathered p,p'-DDE (p,p'-dichlorodiphenyldichloroethylene) by Cucurbita subspecies. The effects of two soil amendments, mycorrhizae or a biosurfactant, on p,p'-DDE accumulation was determined. Also, p,p'-DDE uptake was assessed during plant growth (12, 26, 38, and 62 d), and cultivars that accumulate weathered p,p'-DDE were intercropped with cultivars known not to have that ability. Cucurbita pepo L. ssp. pepo accumulated large amounts of the contaminant, having stem bioconcentration factors, amounts of p,p'-DDE translocated, and contaminant phytoextraction that were 14, 9.9, and 5.0 times greater than C. pepo L. ssp. ovifera (L.) D.S. Decker, respectively. During 62 d, the stem BCF (bioconcentration factor) for p,p'-DDE in subspecies pepo remained constant and the total amount of contaminant accumulated was correlated with plant biomass (r(2) = 0.86). For subspecies ovifera, the stem BCF was highest at 12 d (1.5) but decreased to 0.39 by 62 d, and p,p'-DDE removal was not correlated with plant biomass. Mycorrhizal inoculation increased p,p'-DDE accumulation by both subspecies by an average 4.4 times. For subspecies pepo, mycorrhizae increased the percentage of contaminant extracted from 0.72 to 2.1%. Biosurfactant amendment also enhanced contaminant accumulation by both subspecies, although treatment reduced subspecies ovifera biomass by 60%. The biosurfactant had no effect on the biomass of subspecies pepo, increased the average contaminant concentration by 3.6-fold, and doubled the overall amount of p,p'-DDE removed from the soil. Soil amendments that enhance the mobility of weathered persistent organic pollutants will significantly increase the amount of contaminant phytoextraction by Cucurbita pepo.

Influence of citric acid amendments on the availability of weathered PCBs to plant and earthworm species.

A series of small and large pot trials were conducted to assess the phytoextraction potential of several plant species for weathered polychlorinated biphenyls (PCBs) in soil (105 microg/g Arochlor 1268). In addition, the effect of citric acid on PCB bioavailability to both plants and earthworms was assessed. Under small pot conditions (one plant, 400 g soil), three cucurbits (Cucurbita pepo ssp pepo [zucchini] and ssp ovifera [nonzucchini summer squash], Cucumis sativus, cucumber) accumulated up to 270 microg PCB/g in the roots and 14 microg/g in the stems, resulting in 0.10% contaminant removal from soil. Periodic 1 mM subsurface amendments of citric acid increased the stem and leaf PCB concentration by 330 and 600%, respectively, and resulted in up to a 65% increase in the total amount of contaminant removed from soil. Although citric acid at 10 mM more than doubled the amount of PCB desorbed in abiotic batch slurries, contaminant accumulation by two earthworm species (Eisenia foetida and Lumbricus terrestris) was unaffected by citric acid at 1 and 10 mM and ranged from 11-15 microg/g. Two large pot trials were conducted in which cucurbits (C. pepo ssp pepo and ssp ovifera, C. sativus) and white lupin (Lupinus albus) were grown in 70 kg of PCB-contaminated soil White lupin was the poorest accumulator of PCBs, with approximately 20 microg/g in the roots and 1 microg/g in the stems. Both C. pepo ssp ovifera (summer squash) and C. sativus (cucumber) accumulated approximately 65-100 microg/g in the roots and 6-10 microg/g in the stems. C. pepo ssp pepo (zucchini) accumulated significantly greater levels of PCB than all other species, with 430 microg/g in the roots and 22 microg/g in the stems. The mechanism by which C. pepo spp pepo extracts and translocates weathered PCBs is unknown, but confirms earlier findings on the phytoextraction of other weathered persistent organic pollutants such as chlordane, p,p'-DDE, and polycyclic aromatic hydrocarbons.

Uptake by cucurbitaceae of soil-Bome contaminants depends upon plant genotype and pollutant properties.

Three Cucurbitaceae, Cucurbita pepo L. subsp. pepo (cv. Black Beauty, true zucchini), Cucurbita pepo L. intersubspecific cross (cv. Zephyr, summer squash), and Cucumis sativis (cv. Marketmore, cucumber), were grown in rhizotrons containing soil contaminated with three classes of highly weathered, hydrophobic organic contaminants: (1) technical chlordane, (2) dichlorodiphenylethanes (DDT and DDD) and -ethene (DDE), (3) polyaromatic hydrocarbons (PAHs), and heavy metal residues. Movement of the contaminants through the soil/plant system was studied by comparing contaminant concentration in the bulk soil, the rhizosphere soil pore water, the xylem sap, and aerial tissue. This permitted, for the first time, calculation of bioconcentration factors (BCFs) based on concentration in the xylem sap versus that in the rhizosphere soil pore water. The bioconcentration factors so determined for the sum of five chlordane residues (two enantiomers of trans-chlordane, TC; two enantiomers of cis-chlordane, CC; and achiral trans-nonachlor, TN) were 36, 40, and 23 for Black Beauty, Zephyr, and Marketmore, respectively. In addition, the xylem sap of each cultivar had a consistent enantioselective profile for some of the chiral chlordane components. For the sum of dichlorodiphenylethanes and -ethene, comparable BCF values were 19, 4, and 0.8, respectively. In the case of PAHs, different BCF patterns among the cultivars were noted for three- versus four-ring compounds. Similarly, movement of heavy metals was cultivar-dependent, with cadmium BCF values 9.5, 3.5, and 0.6for Black Beauty, Zephyr, and Marketmore, respectively; the analogous BCFs for zinc were 9, 11, and 2. Thus, passage from ex planta to in planta regions of the soil/plant system is dependent not only on properties of the plant, but also on those of the pollutant. Such data will provide insight into transport mechanisms of highly hydrophobic organic contaminants, as well as heavy metal contaminants, in the soil/plant system.

Accumulation of weathered polycyclic aromatic hydrocarbons (PAHs) by plant and earthworm species.

Experiments were conducted to assess the bioavailability of polyclycic aromatic hydrocarbons (PAHs) in soil from a Manufactured Gas Plant site. Three plant species were cultivated for four consecutive growing cycles (28 days each) in soil contaminated with 36.3 microg/g total PAH. During the first growth period, Cucurbita pepo ssp. pepo (zucchini) tissues contained significantly greater quantities of PAHs than did Cucumis sativus (cucumber) and Cucurbita pepo ssp. ovifera (squash). During the first growth cycle, zucchini plants accumulated up to 5.47 times more total PAH than did the other plants, including up to three orders of magnitude greater levels of the six ring PAHs. Over growth cycles 2-4, PAH accumulation by zucchini decreased by 85%, whereas the uptake of the contaminants by cucumber and squash remained relatively constant. Over all four growth cycles, the removal of PAHs by zucchini was still twice that of the other species. Two earthworm species accumulated significantly different amounts of PAH from the soil; Eisenia foetida and Lumbricus terrestris contained 0.204 and 0.084 microg/g total PAH, respectively, but neither species accumulated measurable quantities 5 or 6 ring PAHs. Lastly, in abiotic desorption experiments with an aqueous phase of synthetically prepared organic acid solutions, the release of 3 and 4 ring PAHs from soil was unaffected by the treatments but the desorption of 5-6 ring constituents was increased by up to two orders of magnitude. The data show that not only is the accumulation of weathered PAHs species-specific but also that the bioavailability of individual PAH constituents is highly variable.

Influence of nutrient amendments on the phytoextraction of weathered 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene by cucurbits.

Field experiments were conducted to determine the impact of nutrient amendments on the phytoextraction of weathered 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (p,p '-DDE) by eight cultivars of cucurbits over a single growing season. Four cultivars of Cucurbita pepo ssp pepo are accumulators and extract percent level quantities of persistent organic pollutants (POPs), whereas C. pepo ssp ovifera and Cucumis sativus are nonaccumulators. The nonamended accumulators phytoextracted 1.0% of the p,p'-DDE and had a translocation factor of 0.44; however, the nonaccumulators removed 0.16% of the contaminant and had a translocation factor value of 0.09. The accumulators also had 3.8 times greater inorganic element content than the nonaccumulators. Duplicate mounds of each cultivar also received weekly nutrient amendments of phosphorus (400 mg/L K2HPO4), nitrogen (200 mg/L KNO3), or nitrogen/phosphorus (400 mg/L K2HPO4, 200 mg/L KNO3); a minus phosphorus treatment involved a 1-L addition of 1 g/L AlSO4 to the soil before planting. When normalized to respective control values (unamended vegetation), the root and stem p,p'-DDE bioconcentration factors (BCF) of the accumulator cultivars were significantly greater than those of the nonaccumulator cultivars under most nutrient regimes. The biomass of accumulator cultivars decreased by up to 61% under certain nutrient regimes, resulting in mixed effects on the amount of p,p'-DDE extracted. Treatment with N and P increased nonaccumulator biomass by 40 to 100%, and increased p,p'-DDE extraction from soil by 75%. Although generally assumed that fertilizer amendments will enhance phytoremediation, as evidenced here by the nonaccumulators, additions of macronutrients may reduce the phytoextraction of weathered POPs by C. pepo ssp pepo. These findings support our hypothesis that the ability of C. pepo ssp pepo to remove sequestered organic contaminants is governed by unique nutrient-acquisition mechanisms.