Is Cystogastrostomy a Definitive Operation for Pancreatitis Associated Pancreatic Fluid Collections?

BACKGROUND: Pancreatic-enteric drainage procedures have become standard therapy for symptomatic pancreatic pseudocysts and walled-off pancreatic necrosis. The need for pancreatic resection after cyst-enteric drainage procedure in the event of recurrence is not well studied. This study aimed to quantify the percentage of patients requiring resection due to recurrence after surgical cystogastrostomy and identify predictors of drainage failure. METHODS: A single-institution retrospective review was conducted to identify all patients undergoing surgical cystogastrostomy between 2012 and 2020. Demographic, disease, and treatment characteristics were identified. Failure of surgical drainage was defined as the need for subsequent pancreatic resection due to recurrence. Characteristics between failure and nonfailure groups were compared with identifying predictors of treatment failure. RESULTS: Twenty-four cystogastrostomies were performed during the study period. Three patients (12.5%) required a subsequent distal pancreatectomy after surgical drainage. There was no difference in comorbidities between drainage alone and failure of drainage groups. Mean cyst size seemed to be larger in patients that underwent drainage alone versus those that needed subsequent resection (15.2 vs 10.3 cm, P =0.05). Estimated blood loss at initial operation was similar between groups (126 vs 166 mL, P =0.36). CONCLUSION: Surgical pancreatic drainage was successful in the initial management of pancreatic fluid collections. We did not identify any predictors of failure of initial drainage. There was a trend suggesting smaller cyst size may be associated with cystgastrostomy failure. Resection with distal pancreatectomy for walled-off pancreatic necrosis and pancreatic pseudocysts can be reserved for cases of failure of drainage.

Hiatal Hernia After Esophagectomy: A Single-Center Retrospective Analysis of a Rare Postoperative Phenomenon.

Development of a post-esophagectomy hiatal hernia (PEHH) is a rare, but problematic, sequela with the current reported prevalence ranging up to 20%. To determine the incidence rate of PEHH at our institution, a retrospective review of all transhiatal esophagectomies performed from 2012 to 2020 was conducted. Demographic, operative, and oncologic data were collected, rates of PEHH were calculated, and characteristics of subsequent repair were reviewed and analyzed. A total of 160 transhiatal esophagectomies were included, of which four patients (2.5%) developed a PEHH at a mean of 12 months postoperatively (range: 3-28 months) with symptomatology driving the diagnosis for three patients. The limited size of our study does not allow for statistically significant determinations regarding risk factors or method of repair. The true prevalence of a hiatal defect is likely higher than reported, as clinically asymptomatic patients are not captured in our current literature.

Esophagectomy in octogenarians: is it at a cost?

Background: Surgical intervention in the geriatric population has a higher risk of perioperative morbidity and mortality due to frailty, comorbidities, and lack of compensatory physiologic reserve. The literature on esophagectomy in octogenarians is limited and there is concern about elderly patients being with-held surgery. The purpose of this study is to analyze the outcomes of esophagectomies for esophageal cancer in octogenarians to assess the safety of esophagectomy in this population. Methods: 145 transhiatal esophagectomies performed for esophageal cancer between 2012 and 2020 were retrospectively reviewed in this IRB approved study. Two aborted esophagectomies were excluded. Patient demographics, surgical outcomes, and oncologic outcomes were reviewed. The octogenarian group was analyzed compared to patients younger than 80 years of age. Results: Among 143 esophagectomies, 136 patients were <80 years old while 7 were ≥80 years old. Octogenarians received significantly less neoadjuvant therapy compared to younger patients (42.9% vs 80.2%, p = 0.02). No statistically significant difference was noted in complication rate, length of stay (LOS), estimated blood loss (EBL), or mortality. However, octogenarians were found to have an increase in severity of complications compared to younger patients. Conclusion: This study demonstrates that esophagectomy can be performed in carefully selected octogenarians. This comes at a cost with increased severity of complications without an increase in complication rates or mortality. This data suggests that esophagectomy can be offered selectively to older patients with clear expectations and planning for the high risk of more severe post-operative complications.

"Infiltrative" Versus "Mass-Forming" Pancreatic Cancer: A New Radiological Classification System for Pancreatic Head Ductal Carcinoma and Its Pathological Correlation.

Purpose: Resectability in localized pancreatic ductal adenocarcinoma (PDAC) is deemed through radiological criteria. Despite initial evaluation classifying tumors as "resectable," they often have ill-defined borders that can result in more extensive cancer than predicted on final pathology analysis. We attempt to categorize these tumors radiologically and define them as "infiltrative" and contrast them to more well-defined or "mass-forming" tumors and assess their correlation with surgical oncological outcomes. We hypothesize that mass-forming lesions will result in fewer positive resection margins. Methods: Patients diagnosed with PDAC of the head of the pancreas and who underwent subsequent curative intent resection between 2016 and 2018 were included. A retrospective chart review of patients was conducted and computed tomography images at the time of diagnosis were reviewed by two radiologists and scored as "mass forming" or "infiltrative" using a newly developed classification system. These classifications were then correlated with margin status. Results: Sixty-eight consecutive pancreatoduodenectomies performed for PDAC from 2016 to 2018 were identified. After screening, 54 patients were eligible for inclusion. Radiologically defined mass-forming lesions had a trend toward a lower rate of positive resection margins (35.7% vs. 50.0%; p = 0.18), specifically the bile duct margin and pancreas margin as well as an overall larger size (4.03 cm vs. 3.25 cm, p = 0.02) compared with infiltrative lesions. Conclusion: We propose a new radiological definition of PDAC into "mass forming" and "infiltrative," a nomenclature that resonates with other tumor sites. Infiltrative lesions trended toward a higher rate of positive resection margins. This classification may help tailor therapy for infiltrative tumors toward a neoadjuvant approach even if they appear resectable.

To Wrap or Not to Wrap After Heller Myotomy.

BACKGROUND AND OBJECTIVES: The primary aim of this study is to assess the necessity of fundoplication for reflux in patients undergoing Heller myotomy for achalasia. The secondary aim is to assess the safety of the robotic approach to Heller myotomy. METHODS: This is a single institution, retrospective analysis of 61 patients who underwent robotic Heller myotomy with or without fundoplication over a 4-year period (January 1, 2015 - December 31, 2019). Symptoms were evaluated using pre-operative and postoperative Eckardt scores at < 2 weeks (short-term) and 4 - 55 months (long-term) postoperatively. Incidence of gastroesophageal reflux and use of antacids postoperatively were assessed. Long-term patient satisfaction and quality of life (QOL) were assessed with a phone survey. Finally, the perioperative safety profile of robotic Heller myotomy was evaluated. RESULTS: The long-term average Eckardt score in patients undergoing Heller myotomy without fundoplication was notably lower than in patients with a fundoplication (0.72 vs 2.44). Gastroesophageal reflux rates were lower in patient without a fundoplication (16.0% vs 33.3%). Additionally, dysphagia rates were lower in patients without a fundoplication (32.0% vs 44.4%). Only 34.8% (8/25) of patients without fundoplication continued use of antacids in the long-term. There were no mortalities and a 4.2% complication rate with two delayed leaks. CONCLUSION: Robotic Heller myotomy without fundoplication is safe and effective for achalasia. The rate of reflux symptoms and overall Eckardt scores were low postoperatively. Great patient satisfaction and QOL were observed in the long term. Our results suggest that fundoplication is unnecessary when performing Heller myotomy.

Evolution in the Treatment of Esophageal Disease at a Single Academic Institution: 2004-2013.

INTRODUCTION: Management of benign and malignant esophageal disease has changed rapidly over the past decade. The aim of this study was to analyze evolution in surgical management of esophageal disease at a single academic medical center during this period. MATERIALS AND METHODS: We reviewed a retrospective cohort of patients who underwent esophagectomy between 2004 and 2013. Patient, institutional, treatment, and outcomes variables were reviewed. RESULTS: 317 patients were analyzed. Median age was 63.5 years; 80% were male. Average inhospital mortality rate was 3.8%. Operative indications changed significantly from 2004 to 2013, with more operations performed for invasive malignancy (77% vs. 95%) and fewer for high-grade dysplasia (12% vs. 3%, P = .008). In 2004, Ivor Lewis esophagectomy was the most common surgical technique, but the three-field technique was the operation of choice in 2013. A minimally invasive approach was used in 19% of cases in 2004 and 100% of cases in 2013 (P < .001). Anastomotic leak ranged from 0% to 21% with no significant difference over the study period (P = .18). Median lymph node harvest increased from seven to 18 nodes from 2004 to 2013 (P = .001). Hospital length of stay decreased from 15 to 8 days (P = .001). In 2013, 79% of patients were discharged to home, compared to 73% in 2004 (P = .04). DISCUSSION: Over the last decade, our treatment of esophageal disease has evolved from a predominantly open Ivor Lewis to a minimally invasive three-field approach. Operations for malignancy have also increased dramatically. Postoperative complications and mortality were not significantly changed, but were consistently low during the latter years of the study.

Laparoscopic ischemic conditioning of the stomach increases neovascularization of the gastric conduit in patients undergoing esophagectomy for cancer.

BACKGROUND AND OBJECTIVES: Gastric ischemic preconditioning has been proposed to improve blood flow and reduce the incidence of anastomotic complications following esophagectomy with gastric pull-up. This study aimed to evaluate the effect of prolonged ischemic preconditioning on the degree of neovascularization in the distal gastric conduit at the time of esophagectomy. METHODS: A retrospective review of a prospectively maintained database identified 30 patients who underwent esophagectomy. The patients were divided into three groups: control (no preconditioning, n = 9), partial (short gastric vessel ligation only, n = 8), and complete ischemic preconditioning (left and short gastric vessel ligation, n = 13). Microvessel counts were assessed, using immunohistologic analysis to determine the degree of neovascularization at the distal gastric margin. RESULTS: The groups did not differ in age, gender, BMI, pathologic stage, or cancer subtype. Ischemic preconditioning durations were 163 ± 156 days for partial ischemic preconditioning, compared to 95 ± 50 days for complete ischemic preconditioning (P = 0.2). Immunohistologic analysis demonstrated an increase in microvessel counts of 29% following partial ischemic preconditioning (P = 0.3) and 67% after complete ischemic preconditioning (P < 0.0001), compared to controls. CONCLUSIONS: Our study indicates that prolonged ischemic preconditioning is safe and does not interfere with subsequent esophagectomy. Complete ischemic preconditioning increased neovascularization in the distal gastric conduit.

Specific gene expression profiles are associated with a pathologic complete response to neoadjuvant therapy in esophageal adenocarcinoma.

BACKGROUND: Predicting treatment response to chemo-radiotherapy (CRT) in esophageal cancer remains an unrealized goal despite studies linking constellations of genes to prognosis. We aimed to determine if specific expression profiles are associated with pathologic complete response (pCR) after neoadjuvant CRT. METHODS: Eleven genes previously associated with esophageal cancer prognosis were identified. Esophageal adenocarcinoma (EAC) patients treated with neoadjuvant CRT and esophagectomy were included. Patients were classified into two groups: pCR and no-or-incomplete response (NR). Polymerase chain reaction was used to evaluate gene expression. Omnibus testing was applied to overall gene expression differences between groups, and log-rank tests compared individual genes. RESULTS: Eleven pCR and eighteen NR patients were analyzed. Combined expression profiles were significantly different between pCR and NR groups (p < 0.01). The gene CCL28 was over-expressed in pCR patients (Log-HR: 1.53, 95%CI: 0.46-2.59, p = 0.005), and DKK3 was under-expressed in pCR (Log-HR: -1.03 95%CI: -1.97, -0.10, p = 0.031). CONCLUSION: EAC tumors that demonstrated a pCR have genetic profiles that are significantly different from typical NR profiles. The genes CCL28 and DKK3 are potential predictors of treatment response.

Surgical Treatment of High-Grade Dysplasia and Early Esophageal Cancer.

BACKGROUND: The treatment of early-stage esophageal cancer and high-grade dysplasia of the esophagus has changed significantly in recent years. Many early tumors that were traditionally treated with esophagectomy can now be resected with endoscopic therapy alone. These new endoscopic modalities can offer similar survival outcomes without the associated morbidity of a major operation. However, a number of these cases may still require surgical intervention as the best treatment option. METHODS: The current scientific literature, national and international guidelines were reviewed for recommendations regarding optimal treatment of early esophageal malignancy. RESULTS: The primary advantage of surgery over endoscopic treatment lies in the reduced risk of recurrence as well as the ability to assess harvested lymph nodes for regional disease. We recommend that esophageal tumors that have invaded into the submucosa (T1b) or beyond should be treated with an esophagectomy. In addition, dysplastic lesions and cancers that demonstrate poorly differentiated pathology or lymphovascular or perineural invasion should be surgically resected. Finally, large tumors, multifocal lesions, tumors within a long segment of Barrett's esophagus, tumors adjacent to a hiatal hernia, tumors that cannot be resected enbloc with endoscopic techniques should also be treated with an esophagectomy. CONCLUSIONS: When performed at high-volume centers in experienced hands, esophagectomy can have consistently good outcomes for high-grade dysplasia and early esophageal cancers, and should be considered as a treatment option.

Neutrophil-to-Lymphocyte and Platelet-to-Lymphocyte Ratios can Predict Treatment Response to Neoadjuvant Therapy in Esophageal Cancer.

INTRODUCTION: We hypothesized that serum neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios may predict pathologic complete response to neoadjuvant chemoradiotherapy in esophageal cancer patients. The ability to predict favorable treatment response to therapy may aid in determining optimal treatment regimens. MATERIALS AND METHODS: A retrospective review of a prospective esophageal disease registry was conducted. Neutrophil-to-lymphocyte ratio was defined as the pre-chemoradiotherapy serum neutrophil count divided by lymphocyte count. Platelet-to-lymphocyte ratio was similarly defined. Logistic regression was applied to analyze these ratios and their effect on pathologic complete response. A Cox proportional-hazards model was used to analyze survival. RESULTS: Sixty patients were included. Elevated neutrophil-to-lymphocyte ratio and platelet-to-lymphocyte ratio were both negative predictors of pathologic complete response (odds ratio: 0.62; 95% confidence interval: 0.37-0.89, P = 0.037 and odds ratio: 0.91; 95% confidence interval: 0.82-0.98, P = 0.028, respectively). Only platelet-to-lymphocyte ratio was predictive of decreased overall survival (hazard ratio: 1.05, 95% confidence interval: 0.94-1.16, P = 0.40). CONCLUSION: Elevated neutrophil and platelet-to-lymphocyte ratios were significant predictors of a poor treatment response to neoadjuvant therapy. Only elevated platelet-to-lymphocyte ratio was predictive of worse overall survival. Neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios may offer a simple serum test to assess the likelihood of a pathologic complete response after neoadjuvant therapy in esophageal cancer.

Esophagectomy as a Treatment Consideration for Early-Stage Esophageal Cancer and High-Grade Dysplasia.

In recent years, a number of endoluminal procedures such as endoscopic resection and thermal ablation have emerged as less invasive treatment options for early esophageal cancer. These therapies have demonstrated excellent oncologic outcomes for dysplasia as well as intramucosal cancers. However, few studies have directly compared long-term outcomes of endoscopic therapy versus traditional esophagectomy. Current esophagectomy techniques now deliver consistently good outcomes in the hands of experienced surgeons at high volume centers, and this option should be considered an important treatment consideration for early esophageal cancer. Under current recommendations, esophagectomy should be considered for tumors invading the submucosa, tumors with high-risk pathologic features, bulky tumors, multinodular tumors, tumors within a long segment of Barrett's esophagus, and tumors adjacent to a hiatal hernia. Likewise, individual patient factors and comorbidities must also be considered when determining the best treatment for a patient with early esophageal cancer. The risk of missing metastatic disease or recurrence that is associated with endoscopic treatment must be weighed against the surgical risks of esophagectomy. With these considerations in mind, the aim of this article is to review the current guidelines and literature that explore the role of esophagectomy for early esophageal malignancy in the era of endoscopic therapies.

Identifying belief targets to increase bone marrow registry participation among students who have never donated blood.

New members on bone marrow registries worldwide are needed to allow sufficient diversity in the donor pool to meet patient needs. We used the theory of planned behaviour belief-basis and surveyed students who had not donated blood previously (i.e. non-donors) (N = 150) about the behavioural, normative, and control beliefs informing their intentions to join the Australian Bone Marrow Donor Registry. Key beliefs predicting non-donors' intentions included: viewing bone marrow donation as an invasion of the body (ß = -.35), normative support from parents (ß = .40), anticipating pain/side effects from giving blood (ß = -.27), and lack of knowledge about how to register (ß = -.30). Few non-donors endorsed these beliefs, suggesting they are ideal targets for change in strategies encouraging bone marrow donor registration.

A single, global patient-centered measure from the SF-36 instrument to assess surgical outcomes and quality of life: a pilot study.

BACKGROUND: Many quality of life (QoL) and patient-reported outcomes (PRO) measures have been developed to assess the effects of disease processes and treatments. Although these instruments are valuable, the process is hampered because of their number and lack of interchangeability. METHODS: We identified a cohort of patients across a variety of operations within 3-12 months postoperatively. Patients completed the SF-36, measuring eight domains of QoL (physical functioning, role-physical, role-emotional, bodily pain, vitality, mental health, social functioning, and general health), plus a health transition item: Compared to one year ago, how would you rate your health in general now?. (1) Much better now than one year ago. (2) Somewhat better now than one year ago. (3) About the same as one year ago. (4) Somewhat worse than one year ago. (5) Much worse than one year ago. Additional data included improvement of preoperative symptoms, the occurrence of any postoperative symptoms, and the occurrence of any postoperative complications. RESULTS: Of 217 patients, 28 % were much better, 28 % somewhat better, 27 % unchanged, 13 % somewhat worse, and 3 % much worse. The health transition results were associated with all SF-36 domains, preoperative symptom change (p = 0.03) and persistent or new postoperative symptoms (p = 0.001), but not postoperative complications. Patients with persistent or new symptoms postoperatively had worse scores in the role-emotional (p = 0.01), bodily pain (p = 0.05), social functioning (p = 0.02), and mental health (p = 0.009) domains of the SF-36. CONCLUSIONS: This single, global assessment of health transition may be a promising practical alternative to assess postoperative patient-centered outcomes. Improved patients had better QoL scores, preoperative symptoms elimination, and no operation-related symptoms, but the occurrence of complications did not affect improvement.

Exploring the role of gender and risk perceptions in people's decisions to register as a bone marrow donor.

Increasing the number of bone marrow (BM) donors is important to ensure sufficient diversity on BM registries to meet the needs of patients. This study used an experimental approach to test the hypothesis that providing information about the risks of BM donation to allay unsubstantiated fears would reduce male and female participants' perceptions of risk for donation and joining the Australian Bone Marrow Donor Registry (ABMDR). Males' and females' intentions to register on the ABMDR and their attitudes, norms and perceived behavioural control (efficacy) in relation to registering were also explored. Participants were allocated randomly to either a risk (exposed to risk information about BM donation) or no-risk (not exposed to risk information) condition. In partial support of hypotheses, exposure to risk information did reduce perceived risk for registering on the ABMDR for males only. Participants in the risk condition also demonstrated lower scores on attitude (males only) and intention compared with participants in the no-risk condition. These findings highlight the complex role of risk perceptions and gender differences in understanding people's decisions to join a BM registry.

Ultrasonographic evaluation of sinusitis during microgravity in a novel animal model.

OBJECTIVES: To develop an animal model of rhinosinusitis in microgravity, to characterize the behavior of intracavitary fluid in microgravity, and to assess the accuracy of ultrasonographic (US) diagnosis in microgravity. DESIGN: An animal model of acute sinusitis was developed in anesthetized swine by creating a window into a frontal sinus to allow unilateral catheter placement and injection of fluid. We performed US examinations in normal and microgravity environments on control and sinusitis conditions and recorded these for later interpretation. SETTING: Henry Ford Hospital and the National Aeronautics and Space Administration (NASA) Microgravity Research Facility in Houston, Texas. SUBJECTS: Ground (normal-gravity) experiments were conducted on anesthetized swine (n = 4) at Henry Ford Hospital before the microgravity experiments (n = 4) conducted in the NASA Microgravity Research Facility. MAIN OUTCOME MEASURE: Ultrasound visualization of fluid cavity. RESULTS: Results of bilateral US examinations before fluid injection demonstrated typical air-filled sinuses. After unilateral injection of 1 mL of fluid, a consistent air-fluid interface was observed on the catheterized side at ground conditions. Microgravity conditions caused the rapid (<10-second) dissolution of the air-fluid interface, associated with uniform dispersion of the fluid to the walls of the sinus. The air-fluid interface reformed on return to normal gravity. CONCLUSIONS: The US appearance of fluid in nasal sinuses during microgravity is characterized in the large animal model. On the introduction of microgravity, the typical air-fluid interface disassociates, and fluid lining the sinus can be observed. Such fluid behavior can be used to develop diagnostic criteria for acute bacterial rhinosinusitis in the microgravity environment.

Sediment trend analysis of the Hylebos Waterway: implications for liability allocations.

Sediment trend analysis (STA) is a technique that determines the net patterns of sediment movement and their dynamic behavior or stability. The data required are the complete particle size distributions obtained from bottom grab samples collected in a regular grid over the area of interest. Appendix 1 provides the particular details of how STA is undertaken. Because many contaminants are known to associate with the natural particles contained in sedimentary deposits, STA can provide additional weight-of-evidence in ecological risk assessment, remedial investigation, remediation itself, and litigation issues. The STA was applied to 242 sediment samples collected from the Hylebos Waterway, Tacoma, Washington, USA, in support of remedial action planning, contaminant source identification, and ultimately allocation of legal liability for contamination. The Waterway itself comprises a narrow shipping channel extending 3 miles from Commencement Bay (Puget Sound) where it ends in a dredged turning basin (Upper Turning Basin). A 2nd dredged turning basin (Lower Turning Basin) is located about three-quarters of the distance down its length. Both sides of the channel are home to an extensive industrial complex associated with significant contaminant releases into the water. The area was declared a Superfund Site in the early 1980s. The results of the STA showed a consistent pattern of sediment transport directed from the mouth of the Waterway to the turning basin at its head. Divided into 5 separate transport environments (TEs), the sediments within the Waterway progress from transport in Dynamic Equilibrium near the mouth, to Total Deposition (type 1) in the vicinity of the Lower Turning Basin, followed by Total Deposition (type 2) in the Upper Turning Basin. Assuming that contaminants associate preferentially with the finer, rather than the coarser, components of the grain size distributions, a probable behavior of contaminants that can be contained in the sediments is proposed for each TE. Maps showing the spatial distributions of existing contaminant data appear to conform very well to the patterns that might be expected from the STA results. This evidence was primarily used to demonstrate that potentially responsible parties (PRPs) located at the head of the Waterway could not be responsible for contaminated sediments toward its mouth. The findings, for example, effectively dismissed the assumption by the Natural Resource Damage Trustee agencies that contaminated sediments from a particular source would be as likely to migrate down the Waterway as up the Waterway. As a result, major documented sources of contamination near the mouth should be expected to bear a larger share of the total cleanup compared with sources farther toward the head. Furthermore, the STA provided explanations for apparent anomalies such as how hot spots of polychlorinated biphenyls (PCBs) could be located near a property where PCBs had never been released into the environment. If sediment gradient pattern analysis alone were used to allocate liability among PRPs, those located near such hot spots would receive a disproportionate share of liability.

Impact of offsite sediment transport and toxicity on remediation of a contaminated estuarine bay.

Sediment of Ostrich Bay, an arm of Dyes Inlet on Puget Sound, was historically contaminated with ordnance compounds from an onshore US Navy facility. An initial recommendation for a sediment cover to mitigate benthic risks was followed by studies of sediment transport and deposition to determine whether contaminated sediment from Dyes Inlet or other offsite sources in Puget Sound may contribute to Ostrich Bay impacts. A Sediment Trend Analysis (STA) identified net sediment transport pathways throughout the bay and inlet by examining changes in grain size distributions in multiple adjacent samples. Results indicated that fine-grained sedimentary material transports into and deposits throughout the Dyes Inlet system, with no erosion or transport out of Ostrich Bay. Echinoderm larvae mortality bioassay results were elevated in fine-grained sediments of both Ostrich Bay and Dyes Inlet. Ordnance compounds were undetected, and although sediment mercury concentrations were elevated at 0.48-1.4 mg/kg in both waterbodies, the relationship with toxicity was weak. Results of the studies and sedimentation modeling indicate that impacted sedimentary material deposits throughout the Dyes Inlet/Ostrich Bay system from unknown sources and will prevent natural recovery of Ostrich Bay as well as negate long-term effectiveness of active remedial measures. Stakeholders have recognized that remediation of the bay can be achieved only after the toxicity of depositing sediment decreases.