A web-based pesticide risk assessment tool for drinking water protection zones in Sweden.

To protect human health, wildlife and the aquatic environment, "safe uses" of pesticides are determined at the EU level while product authorization and terms of use are established at the national level. In Sweden, extra precaution is taken to protect drinking water, and permits are therefore required for pesticide use within abstraction zones. This paper presents MACRO-DB, a tool for assessing pesticide contamination risks of groundwater and surface water, used by authorities to support their decision-making for issuing such permits. MACRO-DB is a meta-model based on 583,200 simulations of the physically-based MACRO model used for assessing pesticide leaching risks at EU and national level. MACRO-DB is simple to use and runs on widely available input data. In a qualitative comparative assessment for two counties in Sweden, MACRO-DB outputs were in general agreement with groundwater monitoring data and matched or were more protective than the national risk assessment procedure for groundwater.

Ethics Education in U.S. Allopathic Medical Schools: A National Survey of Medical School Deans and Ethics Course Directors.

AbstractPurpose: to characterize ethics course content, structure, resources, pedagogic methods, and opinions among academic administrators and course directors at U.S. medical schools. METHOD: An online questionnaire addressed to academic deans and ethics course directors identified by medical school websites was emailed to 157 Association of American Medical Colleges member medical schools in two successive waves in early 2022. Descriptive statistics were utilized to summarize responses. RESULTS: Representatives from 61 (39%) schools responded. Thirty-two (52%) respondents were course directors; 26 (43%) were deans of academic affairs, medical education, or curriculum; and 3 with other roles also completed the survey (5%). All 61 schools reported some form of formal ethics education during the first year of medical school, with most (n = 54, 89%) reporting a formal mandatory introductory course during preclinical education. Schools primarily utilized lecture and small-group teaching methods. Knowledge-based examinations, attendance, and participation were most commonly used for assessment. A large majority regarded ethics as equally or more important than other foundational courses, but fewer (n = 37, 60%) provided faculty training for teaching ethics. CONCLUSIONS: Despite a response rate of 39 percent, the authors conclude that medical schools include ethics in their curricula in small-group and lecture formats with heterogeneity regarding content taught. Preclinical curricular redesigns must innovate and implement best practices for ensuring sound delivery of ethics content in future curricula. Additional large-scale research is necessary to determine said best practices.

Cutaneous heat and light-induced pain thresholds in post-traumatic headache attributed to mild traumatic brain injury.

OBJECTIVE: The purpose of this study was to characterize cutaneous heat and light-induced pain thresholds in people with post-traumatic headache (PTH) compared with healthy controls (HCs). BACKGROUND: Photophobia and allodynia are common in PTH, and there is emerging evidence to support multimodal sensory dysfunction. METHODS: In this age- and sex-matched cohort study, individuals with PTH (n = 20) and HCs (n = 20), aged 18-65 years, were recruited from an institutional database of research volunteers, from the concussion clinic, and via the use of approved flyers posted on the Mayo Clinic Campus in Scottsdale, Arizona. Participants were assessed using the Allodynia Symptom Checklist (ASC-12), Photosensitivity Assessment Questionnaire (PAQ), State Trait Anxiety Inventory (STAI), and Beck Depression Inventory (BDI). Quantitative sensory testing quantified heat pain thresholds. A light stimulation device quantified light-induced pain thresholds. Subsequently, heat pain thresholds were obtained immediately, 10, and 40 min after a bright light stressor. RESULTS: The mean photophobia symptom severity score, based on the PAQ, was higher in participants with PTH compared with HCs, mean 0.62 (SD = 0.25) versus mean 0.24 (SD = 0.24), p < 0.001. Light-induced pain thresholds were lower in participants with PTH (median = 90.5 lux and quartiles = 17.8 to 378.5) compared with HCs (median = 863.5 lux and quartiles = 519.9 to 4906.5) and were independent from BDI and STAI (p < 0.001). Allodynia scores did not differ between participants with PTH and HCs after adjusting for BDI and STAI scores. Baseline forehead heat pain thresholds were not different, participants with PTH mean 41.9°C (SD = 0.89) versus HCs mean 44.3°C (SD = 0.89), p = 0.061; however, forearm heat pain thresholds were lower in participants with PTH compared with HCs, mean 40.8°C (SD = 0.80) versus mean 44.4°C (SD = 0.80), p = 0.002. The forehead heat pain threshold change from baseline post bright light stressor in participants with PTH versus HCs was different immediately (mean -1.2 (SD = 0.53), p = 0.025), 10 min (mean -1.8 (SD = 0.74), p = 0.015), and 40 min (mean -1.8 (SD = 0.88), p = 0.047). The forearm heat pain threshold change immediately post bright light stressor in participants with PTH versus HCs was different, mean -1.9°C (SD = 0.58), p = 0.001, however, not different at 10 and 40 min. CONCLUSIONS: Photophobia is higher and light-induced pain thresholds are lower in participants with PTH. Exposure to a light stressor reduced heat pain thresholds in participants with PTH immediately post bright light stressor, but not in HCs. This study provides evidence for multimodal sensory dysfunction in people with PTH.

A framework for modelling soil structure dynamics induced by biological activity.

Soil degradation is a worsening global phenomenon driven by socio-economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil-crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil-plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil-crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil.

The PUG Flap: Conjoined Profunda Artery Perforator and Upper Gracilis Flap for Breast Reconstruction.

Abdominal-based free flaps are the mainstay of autologous breast reconstruction; however, the region may not be ideal for patients with inadequate soft tissue or history of abdominal surgery. This case describes the use of a novel conjoined flap based on the profunda artery perforator and upper gracilis pedicles, named the perforator and upper gracilis (PUG) flap. This flap design aims to maximize medial thigh flap volume while ensuring robust tissue perforation. Here, we present our experience with the PUG flap in a breast cancer patient undergoing autologous reconstruction. The patient was a 41-year-old woman seeking nipple-sparing mastectomy and immediate autologous reconstruction with the PUG flap due to limited abdominal tissue availability. The gracilis and profunda artery perforator flaps were elevated using one boomerang-style skin paddle. Once harvested, the flaps were inset with antegrade and retrograde flow off the internal mammary arteries and both respective internal mammary veins. The donor site was closed in a V-Y pattern resulting in a thigh lift-type lift and concealed scar. In conclusion, the boomerang-style PUG flap maximizes medial thigh free tissue transfer volume, offers internal blood flow redundancy, and maintains good cosmesis of the donor site.

A Scoping Review of Mobile Apps in Plastic Surgery: Patient Care, Trainee Education, and Professional Development.

Over the past 10 years, smartphones have become ubiquitous, and mobile apps serve a seemingly endless number of functions in our everyday lives. These functions have entered the realm of plastic surgery, impacting patient care, education, and delivery of services. This article reviews the current uses of plastic surgery mobile apps, app awareness within the plastic surgery community, and the ethical issues surrounding their use in patient care. Methods: A scoping review of electronically available literature within PubMed, Embase, and Scopus databases was conducted in two waves in November and May 2022. Publications discussing mobile application use in plastic surgery were screened for inclusion. Results: Of the 80 nonduplicate publications retrieved, 20 satisfied the inclusion criteria. Articles acquired from the references of these publications were reviewed and summarized when relevant. The average American Society of Plastic Surgeons evidence rating of the publications was 4.2. Applications could be categorized broadly into three categories: patient care and surgical applications, professional development and education, and marketing and practice development. Conclusions: Mobile apps related to plastic surgery have become an abundant resource for patients, attending surgeons, and trainees. Many help bridge gaps in patient care and surgeon-patient communication, and facilitate marketing and practice development. Others make educational content more accessible to trainees and performance assessment more efficient and equitable. The extent of their impact on patient decision-making and expectations has not been completely elucidated.

High-Grade Colonic Stricture After a Severe Case of COVID-19 Pneumonia.

Extrapulmonary involvement of coronavirus-19 disease (COVID-19) is being documented and studied at an increasing frequency. Specifically, gastrointestinal involvement is hypothesized to occur due to cellular entry via the ACE2 receptor found in gastrointestinal epithelial cells, causing inflammation and symptoms such as abdominal pain, nausea/vomiting, and diarrhea. We present the case of a 45-year-old female with recent severe COVID-19 infection and early gastrointestinal symptoms who later presented with worsening abdominal pain, nausea, vomiting, and constipation after initial discharge. She was diagnosed with a large bowel obstruction and underwent urgent exploratory laparotomy, which revealed a stricture of the distal transverse colon. Following segmental resection, the patient experienced resolution of symptoms. We hypothesize that this patient's colonic stricture arose secondary to severe COVID-19-induced bowel inflammation.

Modeling spatial variation in microbial degradation of pesticides in soil.

Currently, no general guidance is available on suitable approaches for dealing with spatial variation in the first-order pesticide degradation rate constant k even though it is a very sensitive parameter and often highly variable at the field, catchment, and regional scales. Supported by some mechanistic reasoning, we propose a simple general modeling approach to predict k from the sorption constant, which reflects bioavailability, and easily measurable surrogate variables for microbial biomass/activity (organic carbon and clay contents). The soil depth was also explicitly included as an additional predictor variable. This approach was tested in a meta-analysis of available literature data using bootstrapped partial least-squares regression. It explained 73% of the variation in k for the 19 pesticide-study combinations (n = 212) in the database. When 4 of the 19 pesticide-study combinations were excluded (n = 169), the approach explained 80% of the variation in the degradation rate constant. We conclude that the approach shows promise as an effective way to account for the effects of bioavailability and microbial activity on microbial pesticide degradation in large-scale model applications.

Vascularized omental lymphatic transplant for upper extremity lymphedema: A systematic review.

BACKGROUND: Vascularized omental lymphatic transplant (VOLT) is an increasingly popular treatment of extremity lymphedema given its promising donor site. While the success of VOLT in the treatment of lymphedema has been reported previously, several questions remain. AIM: To further elucidate appropriate use of VOLT in the treatment of lymphedema, specifically addressing patient selection, harvest technique, and operative methods. METHODS AND RESULTS: A systematic review of VOLT for upper extremity lymphedema was performed. Of 115 yield studies, seven were included for analysis based on inclusion and exclusion criteria. Included studies demonstrated significant reductions in extremity circumference/volume (average volume reduction, 22.7%-39.5%) as well as subjective improvements using patient-reported outcomes. Though studies are heterogenous and limited, when analyzed in aggregate, suggest the efficacy of VOLT in lymphedema treatment. CONCLUSION: This is the largest systematic review of VOLT to date. VOLT continues to show promise as a safe and efficacious surgical intervention for lymphedema in the upper extremity. Further studies are warranted to more definitively identify patients for whom this technique is appropriate as well as ideal harvest and inset technique.

Population study about the attitude toward organ xenotransplantation in the population from Eastern Europe resident in southeast Spain.

BACKGROUND: The objective of this paper is to analyze the attitude toward xenotransplantation and to determine the variables that influence this attitude in the population of southeast Spain who were born in Eastern European countries. METHODS: A random sample was taken of natives from Eastern Europe residing in southeast Spain (n=320). The sample was obtained randomly between November 2005 and April 2006 and stratified according to the respondents' nationality. Attitude was evaluated using a validated questionnaire which was self-administered and completed anonymously. The control group was a random sample of the native Spanish population (n=250). The statistical analysis used included Student's t-test, the chi-square test, Fisher's exact test, and a logistic regression analysis. RESULTS: The questionnaire completion rate was 83% (n=267). Regarding the use of animal organs for transplantation in humans, if the outcome were similar to that achieved when using human organs, 43% (n=114) would be in favor, 32% (n=86) undecided, and the remaining 25% (n=67) would be against it. This attitude is less favorable than in the control group (43% versus 74%, p<0.001). The attitude was related to the following factors: 1) the country of origin (p<0.001); 2) participation in social help activities (p<0.001); 3) discussion on organ donation and transplantation within the family (p=0.005); 4) previous experience of organ donation and transplantation (p=0.002); 5) the respondent's religion (p=0.002); 6) knowing that one's partner had a favorable attitude toward transplantation (p<0.001); 7) the respondent's belief that he or she might need a transplant in the future (p<0.001); 8) the attitude toward human donation, both from cadaver (p<0.001) and living (p<0.001) donors. The following were also independent variables in the subsequent multivariate analysis: 1) favorable attitude toward cadaver organ donation (OR=4.998); 2) previous experience of donation (0R=2.857); 3) partner's attitude against transplantation (OR=0.079); and 4) attitude toward living donation (OR=12. 703). CONCLUSIONS: The attitude toward xenotransplantation is less positive among Eastern Europeans living in Spain than in the native Spanish population and is influenced by many psychosocial factors that are mainly related to human organ donation.

Factors that influence the attitude of East European residents in Spain towards living kidney donation.

UNLABELLED: Emigration from East European (EE) countries into the South East of Spain (SES) is becoming more common. The objective of this study was to analyse the attitude towards living kidney donation in this group. A sample of residents (n = 320) in the SES who come from EE was obtained randomly and stratified by a respondent's nationality (November-05 to April-06). Attitude was evaluated using a validated questionnaire that was completed anonymously and was self-administered. CONTROL GROUP: native Spanish citizens. The questionnaire completion rate was 83% (n = 265). A total of 83% (n = 220) were in favor of related living donation. Attitude is similar to that of the urban control group (P = 0.0534) and more positive than that prevalent in the rural setting (P < 0.001). The variables that were related to attitude included: a respondent's marital status (P < 0.001); the country of origin (P = 0.014); attitude towards deceased donation (P < 0.001); having discussed the subject within the family (P < 0.001); a respondent's belief that he might need a transplant organ (P = 0.002) and concern about possible 'mutilation' after donation (P < 0.001). There is a favorable attitude towards related living kidney donation among EE who are resident in the SES and this attitude is closely related to attitude towards deceased donation, the attitude of one's family and feelings of reciprocity.

Attitude of the population of German origin in the south east of Spain toward living kidney donation. In search of favorable sub-groups for promoting living kidney donation in Spain.

BACKGROUND: There is an increasing population of German origin living in the South East of Spain. OBJECTIVE: To analyze the attitude toward living kidney donation in this population subgroup. METHODS: A sample of German residents in the South East of Spain was taken randomly (n = 250) (November 2005-April 2006). Attitude was evaluated using a validated questionnaire. The survey was self-administered and completed anonymously. The control group comprised native Spanish citizens (n = 500). RESULTS: The questionnaire completion rate was 87% (n = 218). Most respondents (92%, n = 201) are in favor of living-related donation. The following variables are related to attitude to donation: (1) marital status of the respondent (p = 0.002); (2) level of education (p < 0.001); (3) attitude toward cadaveric donation (p = 0.005); (4) having had previous experience with the donation and transplantation process (p < 0.001); (5) the respondent's religion (p = 0.002); (6) the risk that they believe is involved in living kidney donation (p = 0.001), and (7) concern about 'mutilation' that could be caused by living donation (p < 0.001). CONCLUSIONS: Attitude toward related living kidney donation of German residents in the South East of Spain is favorable and is closely related to attitude toward cadaveric donation, fear of the after-effects of this type of donation and religious attitude.

Identification of key climatic factors regulating the transport of pesticides in leaching and to tile drains.

BACKGROUND: Key climatic factors influencing the transport of pesticides to drains and to depth were identified. Climatic characteristics such as the timing of rainfall in relation to pesticide application may be more critical than average annual temperature and rainfall. The fate of three pesticides was simulated in nine contrasting soil types for two seasons, five application dates and six synthetic weather data series using the MACRO model, and predicted cumulative pesticide loads were analysed using statistical methods. RESULTS: Classification trees and Pearson correlations indicated that simulated losses in excess of 75th percentile values (0.046 mg m(-2) for leaching, 0.042 mg m(-2) for drainage) generally occurred with large rainfall events following autumn application on clay soils, for both leaching and drainage scenarios. The amount and timing of winter rainfall were important factors, whatever the application period, and these interacted strongly with soil texture and pesticide mobility and persistence. Winter rainfall primarily influenced losses of less mobile and more persistent compounds, while short-term rainfall and temperature controlled leaching of the more mobile pesticides. CONCLUSIONS: Numerous climatic characteristics influenced pesticide loss, including the amount of precipitation as well as the timing of rainfall and extreme events in relation to application date. Information regarding the relative influence of the climatic characteristics evaluated here can support the development of a climatic zonation for European-scale risk assessment for pesticide fate.

Meta-analysis of pesticide sorption in subsoil.

Models used to assess leaching risks generally use organic carbon partition coefficient (kOC ) values derived from batch experiments on topsoil samples to estimate pesticide sorption in subsoils of much smaller organic carbon contents. This can introduce significant errors in leaching risk calculations, because inorganic sorbents can play an important role for sorption in subsoil. The objectives of the present study were therefore to summarize the available literature data on pesticide sorption in subsoils and to test whether a simple alternative model could improve on the standard kOC approach used in risk assessment models for pesticide leaching. This model describes the sorption constant as a power law function of the organic carbon content. A database with the results of batch sorption experiments was collated from published studies that emphasized measurements in subsoils. This database contains 1029 data entries from 36 published studies with data for 29 active substances (11 nonionic compounds, 10 weak acids, 6 weak bases, one cation, and one zwitterion). The results show that whereas the constant kOC model proved to be an adequate model for 17 of the 63 individual datasets, the power law model gave acceptable fits (p < 0.05) for 60 of these cases. The exponent in the power law model varied over a wide range, from slightly negative to near unity. It also differed significantly (p = 0.015) for ionized and nonionized compounds, with median values of 0.25 and 0.55, respectively. It is concluded that the power law model could be used to parameterize subsoil sorption in regulatory leaching models, because it has widespread applicability and is simple enough for this purpose. Suitable ways of incorporating this approach in risk assessment procedures are discussed. Environ Toxicol Chem 2018;37:755-761. © 2017 SETAC.

Spatial and temporal patterns of pesticide concentrations in streamflow, drainage and runoff in a small Swedish agricultural catchment.

A better understanding of the dominant source areas and transport pathways of pesticide losses to surface water is needed for targeting mitigation efforts in a more cost-effective way. To this end, we monitored pesticides in surface water in an agricultural catchment typical of one of the main crop production regions in Sweden. Three small sub-catchments (88-242ha) were selected for water sampling based on a high-resolution digital soil map developed from proximal sensing methods and soil sampling; one sub-catchment had a high proportion of clay soils, another was dominated by coarse sandy soils while the third comprised a mix of soil types. Samples were collected from the stream, from field drains discharging into the stream and from within-field surface runoff during spring and early summer in three consecutive years. These samples were analyzed by LC-MS/MS for 99 compounds, including most of the polar and semi-polar pesticides frequently used in Swedish agriculture. Information on pesticide applications (products, doses and timing) was obtained from annual interviews with the farmers. There were clear and consistent differences in pesticide occurrence in the stream between the three sub-catchments, with both the numbers of detected compounds and concentrations being the largest in the area with a high proportion of clay soils and with very few detections in the sandy sub-catchment. Macropore flow to drains was most likely the dominant loss pathway in the studied area. Many of the compounds that were detected in drainage and stream water samples had not been applied for several years. This suggests that despite the predominant role of fast flow pathways in determining losses to the stream, long-term storage along the transport pathways also occurs, presumably in subsoil horizons where degradation is slow.

The effect of freezing and thawing on water flow and MCPA leaching in partially frozen soil.

Limited knowledge and experimental data exist on pesticide leaching through partially frozen soil. The objective of this study was to better understand the complex processes of freezing and thawing and the effects these processes have on water flow and pesticide transport through soil. To achieve this we conducted a soil column irrigation experiment to quantify the transport of a non-reactive tracer and the herbicide MCPA in partially frozen soil. In total 40 intact topsoil and subsoil columns from two agricultural fields with contrasting soil types (silt and loam) in South-East Norway were used in this experiment. MCPA and bromide were applied on top of all columns. Half the columns were then frozen at -3 °C while the other half of the columns were stored at +4 °C. Columns were then subjected to repeated irrigation events at a rate of 5 mm artificial rainwater for 5 h at each event. Each irrigation was followed by 14-day periods of freezing or refrigeration. Percolate was collected and analysed for MCPA and bromide. The results show that nearly 100% more MCPA leached from frozen than unfrozen topsoil columns of Hov silt and Kroer loam soils. Leaching patterns of bromide and MCPA were very similar in frozen columns with high concentrations and clear peaks early in the irrigation process, and with lower concentrations leaching at later stages. Hardly any MCPA leached from unfrozen topsoil columns (0.4-0.5% of applied amount) and concentrations were very low. Bromide showed a different flow pattern indicating a more uniform advective-dispersive transport process in the unfrozen columns with higher concentrations leaching but without clear concentration peaks. This study documents that pesticides can be preferentially transported through soil macropores at relatively high concentrations in partially frozen soil. These findings indicate, that monitoring programs should include sampling during snow melt or early spring in areas were soil frost is common as this period could imply exposure peaks in groundwater or surface water.

Accounting for uncertainty in pedotransfer functions in vulnerability assessments of pesticide leaching to groundwater.

A simulation tool for site-specific vulnerability assessments of pesticide leaching to groundwater was developed, based on the pesticide fate and transport model MACRO, parameterized using pedotransfer functions and reasonable worst-case parameter values. The effects of uncertainty in the pedotransfer functions on simulation results were examined for 48 combinations of soils, pesticides and application timings, by sampling pedotransfer function regression errors and propagating them through the simulation model in a Monte Carlo analysis. An uncertainty factor, f(u), was derived, defined as the ratio between the concentration simulated with no errors, c(sim), and the 80th percentile concentration for the scenario. The pedotransfer function errors caused a large variation in simulation results, with f(u) ranging from 1.14 to 1440, with a median of 2.8. A non-linear relationship was found between f(u) and c(sim), which can be used to account for parameter uncertainty by correcting the simulated concentration, c(sim), to an estimated 80th percentile value. For fine-textured soils, the predictions were most sensitive to errors in the pedotransfer functions for two parameters regulating macropore flow (the saturated matrix hydraulic conductivity, K(b), and the effective diffusion pathlength, d) and two water retention function parameters (van Genuchten's N and alpha parameters). For coarse-textured soils, the model was also sensitive to errors in the exponent in the degradation water response function and the dispersivity, in addition to K(b), but showed little sensitivity to d. To reduce uncertainty in model predictions, improved pedotransfer functions for K(b), d, N and alpha would therefore be most useful.

Testing MACRO (version 5.1) for pesticide leaching in a Dutch clay soil.

Testing of pesticide leaching models against comprehensive field-scale measurements is necessary to increase confidence in their predictive ability when used as regulatory tools. Version 5.1 of the MACRO model was tested against measurements of water flow and the behaviour of bromide, bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] and imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] in a cracked clay soil. In keeping with EU (FOCUS) procedures, the model was first calibrated against the measured moisture profiles and bromide concentrations in soil and in drain water. Uncalibrated pesticide simulations based on laboratory measurements of sorption and degradation were then compared with field data on the leaching of bentazone and imidacloprid. Calibrated parameter values indicated that a high degree of physical non-equilibrium (i.e. strong macropore flow) was necessary to describe solute transport in this soil. Comparison of measured and simulated bentazone concentration profiles revealed that the bulk of the bentazone movement in this soil was underestimated by MACRO. Nevertheless, the model simulated the dynamics of the bentazone breakthrough in drain water rather well and, in particular, accurately simulated the timing and the concentration level of the early bentazone breakthrough in drain water. The imidacloprid concentration profiles and its persistence in soil were simulated well. Moreover, the timing of the early imidacloprid breakthrough in the drain water was simulated well, although the simulated concentrations were about 2-3 times larger than measured. Deep groundwater concentrations for all substances were underestimated by MACRO, although it simulated concentrations in the shallow groundwater reasonably well. It is concluded that, in the context of ecotoxicological risk assessments for surface water, MACRO can give reasonably good simulations of pesticide concentrations in water draining from cracking clay soils, but that prior calibration against hydrologic and tracer data is desirable to reduce uncertainty and improve accuracy.

Meta-modeling of the pesticide fate model MACRO for groundwater exposure assessments using artificial neural networks.

Several simple index methods that use easily accessible data have been developed and included in decision-support systems to estimate pesticide leaching across larger areas. However, these methods often lack important process descriptions (e.g. macropore flow), which brings into question their reliability. Descriptions of macropore flow have been included in simulation models, but these are too complex and demanding for spatial applications. To resolve this dilemma, a neural network simulation meta-model of the dual-permeability macropore flow model MACRO was created for pesticide groundwater exposure assessment. The model was parameterized using pedotransfer functions that require as input the clay and sand content of the topsoil and subsoil, and the topsoil organic carbon content. The meta-model also requires the topsoil pesticide half-life and the soil organic carbon sorption coefficient as input. A fully connected feed-forward multilayer perceptron classification network with two hidden layers, linked to fully connected feed-forward multilayer perceptron neural networks with one hidden layer, trained on sub-sets of the target variable, was shown to be a suitable meta-model for the intended purpose. A Fourier amplitude sensitivity test showed that the model output (the 80th percentile average yearly pesticide concentration at 1 m depth for a 20 year simulation period) was sensitive to all input parameters. The two input parameters related to pesticide characteristics (i.e. soil organic carbon sorption coefficient and topsoil pesticide half-life) were the most influential, but texture in the topsoil was also quite important since it was assumed to control the mass exchange coefficient that regulates the strength of macropore flow. This is in contrast to models based on the advection-dispersion equation where soil texture is relatively unimportant. The use of the meta-model is exemplified with a case-study where the spatial variability of pesticide leaching is mapped for a small field. It was shown that the area of the field that contributes most to leaching depends on the properties of the compound in question. It is concluded that the simulation meta-model of MACRO should prove useful for mapping relative pesticide leaching risks at large scales.