碘缺乏、甲状腺功能减退对仔鼠海马RKC活性及表达的影响

目的 :研究碘缺乏、甲状腺功能减退对仔鼠海马蛋白激酶C活性的影响 ,并测定碘缺乏、甲状腺功能减退大鼠仔鼠海马组织c -fos、c-jun的表达 ,以探讨碘缺乏、甲状腺功能减退调节脑发育的机制。方法 :分别选用低碘饲料及他巴唑诱导建立低碘及甲减大鼠动物模型 ,收集生后 30d时仔鼠海马组织 ,测定海马细胞浆、细胞膜PKC活性。免疫组织化学S -P法染色 ,观察生后 30d时低碘组、甲状腺功能减退组 (甲减组 )及对照组大鼠仔鼠海马c-fos、c -jun表达情况并进行图像分析。结果 :生后 30d低碘组和甲减组仔鼠海马胞液PKC活性略低于对照组 ,而胞膜PKC活性稍高于对照组 ,低碘组、甲减组仔鼠海马胞膜PKC活性与胞浆PKC活性比值 (1. 4 1± 0 .12 ,1. 19± 0 . 14 )较对照组 (0 . 6 5± 0. 0 9)升高 ,差异有统计学意义 (P <0 .0 1)。生后 30天低碘组和甲减组仔鼠海马组织c -fos、c-jun灰度值均显著高于对照组P <0 .0 1) ,提示其表达水平明显降低。结论 :碘缺乏、甲状腺功能减退可引起仔鼠海马胞浆PKC向胞膜的转运 ,并可降低仔鼠海马组织原癌基因c -fos、c-jun表达 ,进而影响神经系统及智力发育 ,可能是低碘、甲减引起海马损害导致学习记忆功能减退的机制之一。     

碘缺乏对大鼠仔鼠海马蛋白激酶C活性的影响

目的研究碘缺乏、甲状腺功能减退对仔鼠海马蛋白激酶C(PKC)活性的影响。方法分别选用低碘饲料及他巴唑诱导建立低碘及甲减大鼠动物模型,在生后第30 d时收集低碘组、甲状腺功能减退组及对照组大鼠仔鼠海马组织,测定海马细胞浆、细胞膜PKC活性。结果生后30 d低碘组和甲状腺功能减退组仔鼠海马胞液PKC活性(24.876 3±13.731 9),(26.342 0±7.302 8)pmol/(min.mg)略低于对照组(36.775 8±15.711 3)pmol/(min.mg);而胞膜PKC活性(33.220 7±18.341 4),(30.177 5±10.443 3)稍高于对照组(20.559 8±6.312 1)pmol/(min.mg),低碘组、甲状腺功能减退组仔鼠海马胞膜PKC活性与胞浆PKC活性比值(1.187 1±0.432 5),(1.414 3±0.394 0)较对照组升高(0.649 3±0.294 3),差异有统计学意义(P<0.01)。结论低碘、甲状腺功能减退可引起仔鼠海马胞浆PKC向胞膜的转运,可能是低碘、甲减引起海马损害导致学习记忆功能减退的机制之一。     

碘缺乏、甲减对仔鼠海马相关酶及蛋白影响

目的 研究碘缺乏、甲状腺功能减退(甲减)对仔鼠海马蛋白激酶C活性的影响,并测定碘缺乏、甲减大鼠仔鼠海马组织c-fos、c-jun的表达,以探讨碘缺乏、甲减调节脑发育的机制.方法 分别选用低碘饲料及他巴唑诱导建立低碘及甲减大鼠动物模型,收集生后30 d时仔鼠海马组织,测定海马细胞浆、细胞膜PKC活性.免疫组织化学S-P法染色,观察生后30d时低碘组、甲减组及对照组大鼠仔鼠海马即早基因c-fos、c-jun表达情况并进行图像分析.结果 生后30 d低碘组和甲减组仔鼠海马胞液PKC活性略低于对照组,而胞膜PKC活性稍高于对照组,低碘组、甲减组仔鼠海马胞膜PKC活性与胞浆PKC活性比值(1.1871±0.4325,1.4143±0.3940)较对照组(0.6493±0.2943)升高,差异有统计学意义(P＜0.01).生后30d低碘组和甲减组仔鼠海马组织c-fos、c-jun灰度值均显著高于对照组(P＜0.0l),提示其表达水平明显降低.结论 碘缺乏、甲状腺功能减退可影响神经系统及智力发育,可能是低碘、甲减引起海马损害导致学习记忆功能减退的机制之一.     

妊娠大鼠碘缺乏和甲状腺功能减退对仔鼠海马神经颗粒素表达的影响

目的观察妊娠大鼠碘缺乏和甲状腺功能减退对仔鼠海马神经颗粒素(neurogranin,Ng/RC3)表达的影响。方法将妊娠清洁级Wistar大鼠28只按体重随机分成对照组、碘缺乏组、甲状腺功能减退1、2组,每组7只。自妊娠第6天(GD6)起,碘缺乏组饲以缺碘地区粮食配制的饲料[碘含量为(14.11±1.96)ng/g],饮用自来水;甲状腺功能减退1、2组分别给予5和15mg/L丙基硫尿嘧啶(propylthiouracil,PTU)溶液作为饮用水,饲喂普通饲料[碘含量为(470.50±46.52)ng/g],直至仔鼠出生后第28天(PN28);对照组饮用自来水,饲喂普通饲料。分别于PN14、PN21、PN28和PN42时,每组随机取5只仔鼠,观察海马CA1、CA3和DG区Ng表达。结果在PN14时,碘缺乏组、甲状腺功能减退1、2组仔鼠海马CA1区Ng蛋白表达水平低于对照组,差异均有统计学意义(P0.05);在PN21时,碘缺乏组、甲状腺功能减退1、2组仔鼠海马CA1区以及碘缺乏组、甲状腺功能减退2组仔鼠海马CA3区Ng蛋白表达水平低于对照组,差异均有统计学意义(P0.05);在PN28时,碘缺乏组、甲状腺功能减退1、2组仔鼠海马CA3区以及碘缺乏组、甲状腺功能减退2组仔鼠海马CA1区Ng蛋白表达水平低于对照组,差异均有统计学意义(P0.05);在PN42时,碘缺乏组、甲状腺功能减退1、2组仔鼠海马CA3区和CA1区Ng蛋白表达水平低于对照组,差异均有统计学意义(P0.05)。结论妊娠大鼠碘缺乏和甲状腺功能减退可降低仔鼠海马CA1和CA3区Ng的表达。     

妊娠大鼠碘缺乏和甲状腺功能减退对仔鼠海马脑源性神经营养因子表达的影响

目的观察妊娠大鼠碘缺乏和甲状腺功能减退对仔鼠海马脑源性神经营养因子(brain-derived neurotrophic factor,BDNF)表达的影响。方法将妊娠清洁级Wistar大鼠28只按体重随机分成对照组、碘缺乏组、甲状腺功能减退1、2组,每组7只。自GD6起,碘缺乏组饲以缺碘地区粮食配制的饲料[碘含量为(14.11±1.96)ng/g],饮用自来水;甲状腺功能减退1、2组分别给予5和15mg/L丙基硫尿嘧啶(propylthiouracil,PTU)溶液作为饮用水,饲喂普通饲料[碘含量为(470.50±46.52)ng/g],直至仔鼠出生后第28天(PN28);对照组饮用自来水,饲喂普通饲料。分别于PN14、PN21、PN28和PN42时,每组随机取5只仔鼠,观察海马CA1、CA3和DG区BDNF表达。结果在PN14时,各组仔鼠海马CA1、CA3和DG区BDNF蛋白表达水平间比较,差异均无统计学意义。在PN21时,甲状腺功能减退2组和碘缺乏组仔鼠海马CA1、CA3和DG区BDNF蛋白表达水平低于对照组,差异均有统计学意义(P0.05);碘缺乏组仔鼠海马CA1区以及甲状腺功能减退2组和碘缺乏组仔鼠海马DG区BDNF蛋白水平低于甲状腺功能减退1组,差异均有统计学意义(P0.05)。在PN28时,甲状腺功能减退2组和碘缺乏组仔鼠海马CA1、CA3和DG区以及甲状腺功能减退1组仔鼠海马CA3区BDNF蛋白表达水平低于对照组,差异均有统计学意义(P0.05);甲状腺功能减退2组和碘缺乏组仔鼠海马CA1区BDNF蛋白表达水平低于甲状腺功能减退1组,差异均有统计学意义(P0.05)。在PN42时,甲状腺功能减退1、2组和碘缺乏组仔鼠海马CA1、CA3和DG区BDNF蛋白表达水平低于对照组,差异均有统计学意义(P0.05);甲状腺功能减退2组和碘缺乏组仔鼠海马CA1和DG区BDNF蛋白表达水平低于甲状腺功能减退1组,差异均有统计学意义(P0.05)。结论妊娠大鼠碘缺乏和甲状腺功能减退可降低仔鼠海马BDNF的表达。     

慢性染铅对海马CA1区LTP及ERK2活性影响

目的　探讨慢性染铅对海马CA1区LTP及ERK2活性的影响。方法　用同心圆电极刺激海马的Schaffer侧支 ,于CA1区用细胞外玻璃电极记录单脉冲刺激引起的群峰电位 (PS) ,观察对照组和染铅组大鼠于高频刺激后PS幅值的变化 ;同时利用WesternBlots方法检测海马CA1区ERK2的活性。结果　HFS前记录的对照组和染铅组的PS幅值无显著性差异 ;HFS后染铅组的PS平均幅值与对照组相比下降了 79% (P <0 0 1) ;染铅组CA1区的ERK2的活性比对照组下降了 2 4 1% (P <0 0 1)。结论　慢性染铅可抑制CA1-LTP的形成 ,同时这种抑制与铅对ERK2活性抑制密切相关     

碘缺乏对子代大鼠不同脑区一氧化氮含量的影响

目的 :　研究胚胎期和新生期碘缺乏、甲状腺功能低下对大鼠不同脑区 (海马、小脑、大脑皮质 )一氧化氮 (NO)含量的影响。方法 :　复制缺碘大鼠动物模型 ,取子代第 2、3胎大鼠各2 4只分别测定大脑匀浆蛋白质和 NO含量。结果 :　胚胎期和新生期碘缺乏、甲状腺功能低下的子鼠尿碘含量、血清 T3 、T4 含量都较正常对照组明显为低 (P<0 .0 1 ) ,有明显的生长发育障碍 (P<0 .0 1 ) ,学习记忆低下 (P<0 .0 1 )。　　子鼠脑 NO含量的测定表明 ,海马 NO含量较正常对照组明显降低 ,差异有显著意义 (1 1 .6 1±2 .3 1 /2 .3 6± 1 .1 8μmol/g prot,P<0 .0 5 )。小脑 NO含量也明显降低 (1 0 .77± 5 .1 6 /4 .70± 1 .95μmol/g Prot,P<0 .0 5 )。大脑皮质 NO含量与对照组比较无明显差异。结论 :　胚胎期和新生期碘缺乏、甲状腺功能低下对子鼠脑组织 NO含量有影响。大脑不同区域对碘缺乏、甲状腺功能低下所致损伤敏感程度不同 ,海马内与 NO有关的代谢异常最明显 ,这一变化可能参与了碘缺乏大鼠学习记忆低下的发病机制。     

碘缺乏和甲状腺功能减退仔鼠海马CaMKⅡ表达的改变

目的观察多功能钙/钙调蛋白依赖性蛋白激酶Ⅱ(CaMKⅡ)在碘缺乏和甲状腺功能减退的大鼠仔鼠海马中蛋白表达的影响。方法健康2月龄雌性Wistar大鼠,交配妊娠后,取孕鼠28只,按体重随机分成对照组、甲状腺功能减退组和碘缺乏组,甲状腺功能减退组根据饮水中含丙基硫尿嘧啶(PTU)剂量分为5和15mg/L组,每组7只孕鼠。分别于出生后(PN)7、14、和21天时,每组随机取5只仔鼠,灌流固定大脑,进行组织病理切片和免疫组化染色,观察分析海马CaMKⅡ表达。结果对照组仔鼠海马CA1、CA3和DG区均呈强阳性染色,在神经元细胞胞浆内充满CaMKⅡ。5、15mg/L和碘缺乏组仔鼠海马免疫反应产物的分布与对照组一致,但与对照组相比染色强度逐渐降低。PN21和PN14时,仔鼠海马CA1、CA3和DG区平均积分光密度在碘缺乏组[PN21:(26.05±4.98)、(30.79±3.22)、(26.40±2.63);PN14:(25.48±4.87)、(44.17±5.91)、(26.41±3.01)]和15mg/L组[PN21:(17.02±2.68)、(24.57±6.62)、(20.18±4.05);PN14:(20.66±3.51)、(34.94±5.09)、(27.32±4.97)]明显低于对照组[PN21:(57.75±13.22)、(65.03±6.20)、(49.39±8.41),P0.05;PN14:(54.08±12.00)、(71.04±5.07)、(78.52±12.42),P0.05]。PN7时,碘缺乏组和15mg/L组仔鼠海马CA1区平均积分光密度在碘缺乏组(25.74±3.33)和15mg/L组(26.89±5.25)明显低于对照组(40.53±3.65),P0.05。结论碘缺乏和甲状腺功能减退可下调海马组织CaMKⅡ蛋白表达。     

慢性染铅对大鼠脑海马齿状回长时程增强的抑制作用及其机理探讨

给刚断乳的大鼠饮用0.2%醋酸铅水90～108d后,测定血铅和脑铅水平、脑海马齿状回LTP的诱发率、神经元内Ca2+浓度和细胞膜和胞液中蛋白激酶C活性,以探讨铅损害学习记忆功能的机理.结果实验组动物血铅(4.76±1.08μmol/L)和脑铅(0.59±0.06μg/g湿重)水平明显高于对照组(分别为0.17±0.08μmol/L和0.06±0.02μg/g湿重)(P＜0.01);诱发的LTP发生率为18.2%(2/11),明显低于对照组的83.3%(10/12)(P＜0.01),发生LTP动物的PS幅值增长率为基线值(按100%计)的120.15±7.15%,明显低于对照组的142.70±15.10%(P＜0.05),另有63.6%(7/11)的动物出现长时程抑制(LTD);染铅大鼠海马神经元的Ca2+浓度、胞膜和胞液PKC活性分别为265.48±53.61mmol/L、1.52±0.40和1.87±0.35nmol/min/mg蛋白,均比对照组(为108.81±26.85mmol/L、0.94±0.33和1.31±0.29nmol/min/mg蛋白)显著升高(P＜0.01).这表明,慢性染铅损害LTP的形成,而海马神经元Ca2+浓度和PKC活性的异常增高可能是重要机理之一.     

妊娠大鼠碘缺乏和甲状腺功能减退对仔鼠内嗅皮质cAMP反应元件结合蛋白表达的影响

目的观察碘缺乏和甲状腺功能减退损伤内嗅皮质对cAMP反应元件结合蛋白(cAMP response element-binding protein,CREB)蛋白表达的影响。方法将28只妊娠清洁级Wistar大鼠按体重随机分成对照组、碘缺乏组、甲状腺功能减退1、2组,每组7只。自妊娠第6天(GD6)起,碘缺乏组饲以缺碘地区粮食配制的饲料[碘含量为(14.11±1.96)ng/g],饮用自来水;甲状腺功能减退1、2组分别给予5和15mg/L丙基硫尿嘧啶(propylthiouracil,PTU)溶液作为饮用水,饲喂普通饲料[碘含量为(470.50±46.52)ng/g],直至仔鼠出生后第28天(PN28);对照组饮用自来水,饲喂普通饲料。分别于PN7、PN14、PN21、PN28和PN42时,每组随机取5只仔鼠,观察内嗅皮质CREB的表达。结果 PN7时,各组仔鼠内嗅皮质CREB表达水平间比较,差异无统计学意义。PN14和PN21时,甲状腺功能减退1组、2组和碘缺乏组仔鼠内嗅皮质CREB表达水平低于对照组,差异均有统计学意义(P0.05)。PN14时,甲状腺功能减退2组和碘缺乏组CREB表达水平低于甲状腺功能减退1组,差异均有统计学意义(P0.05)。PN28和PN42时,甲状腺功能减退2组和碘缺乏组仔鼠内嗅皮质CREB表达水平低于对照组,差异均有统计学意义(P0.05);PN28时,碘缺乏组仔鼠内嗅皮质CREB表达水平低于甲状腺功能减退1组,差异有统计学意义(P0.05)。与对照组比较,甲状腺功能减退1、2组和碘缺乏组内嗅皮质CREB染色强度明显降低。结论妊娠大鼠碘缺乏和甲状腺功能减退可降低仔鼠内嗅皮质CREB表达。     

Calcium intake in the elderly: validation of a dietary questionnaire

Epidemiological studies of calcium and osteoporosis have been hampered by the lack of a suitable tool for assessing calcium intake. This report describes a new frequency and amount questionnaire for measuring present and past calcium intake in the elderly. The validity of the questionnaire was tested against two commonly used standards of dietary assessment, five-day duplicate diets and seven-day weighed dietary inventories. The resulting correlation coefficients were, respectively, r = 0.76 and r = 0.69, while that for repeatability was r = 0.84. Furthermore, the questionnaire categorized subjects into thirds of the distribution of intake with almost no gross misclassification. It is suggested that the present findings may be extended to the majority of normal, healthy elderly subjects, implying wide application for the questionnaire in the assessment of calcium intake in the elderly.     

The occurrence of antimicrobial substances in toilet,sink and shower drainpipes of clinical units: A neglected source of antibiotic residues

Antibiotics represent one of the most important drug groups used in the management of bacterial infections in humans and animals. Due to the increasing problem of antibiotic resistance, assurance of the antibacterial effectiveness of these substances has moved into the focus of public health. The reduction in antibiotic residues in wastewater and the environment may play a decisive role in the development of increasing rates of antibiotic resistance. The present study examines the wastewater of 31 patient rooms of various German clinics for possible residues of antibiotics, as well as the wastewater of five private households as a reference.To the best of our knowledge, this study shows for the first time that in hospitals with high antibiotic consumption rates, residues of these drugs can be regularly detected in toilets, sink siphons and shower drains at concentrations ranging from 0.02?μg·L^?1 to a maximum of 79?mg·L^?1. After complete flushing of the wastewater siphons, antibiotics are no longer detectable, but after temporal stagnation, the concentration of the active substances in the water phases of respective siphons increases again, suggesting that antibiotics persist through the washing process in biofilms. This study demonstrates that clinical wastewater systems offer further possibilities for the optimization of antibiotic resistance surveillance.     

The human drama of genetics: 'hard' and 'soft' media representations of inherited breast cancer

This paper examines media coverage of 'breast cancer genetics', and explores its implications for public understanding. We present a content analysis of coverage in British newspapers and look at a variety of popular forms, including women's magazines, television soap opera and radio drama. Genetic/inherited risk receives a great deal of coverage across a wide range of media formats and outlets. Much of this attention has focused on individuals from 'high risk families' and dilemmas around prophylactic mastectomies. Through examining media coverage, combined with interviews with media personnel and their sources, we show why this story proved so attractive to the media and highlight the different production values which influence coverage. Finally, we introduce preliminary findings from focus group discussions to demonstrate how such 'human interest' framing has engaged audience attention and influenced public understandings. The paper concludes by highlighting the implications for analysing, predicting, and engaging with, media representations of science.     

Self-reported health problems among Swedish miners one year after unemployment

Unemployment is considered to be a public health concern sincedeterioration in the health of the unemployed is often anticipated.However, for some groups, such as miners, unemployment mightimprove health due to a cessation of potentially harmful occupationalexposures. This study evaluates the health of 79 miners in oneSwedish iron-ore mine, and 226 age-matched controls from thegeneral population, during one year after the closure of themine. The participants received a questionnaire regarding medicalhistory and subjective symptoms at the beginning of the studyperiod, and after one year. Statistically significant negativeeffects on self-reported health attributable to unemploymentwere not found, although neuropsychiatric symptoms were morecommon among the unemployed miners. The miners reported a statisticallysignificant improvement in grip force (p=0.031). They had asignificantly higher prevalence of symptoms associated withmining related exposures when compared with the population controls;pain in the upper extremities [relative risk (RR)=2.27, 95%confidence interval (Cl)=1.44–3.59), back pain (RR=1.84;Cl=1.237–2.75), vasospastic disease of the fingers (RR=2.05;Cl=1.18–3.57) and obstructive respiratory symptoms (attacksof dyspnea and wheezing: RR=3.67; Cl=1.167–11.6).     

Excès de cas humains et animaux de tularémie en France au cours de l’hiver 2007–2008 : émergence ou phénomène isolé ?

Context

Tularemia is a zoonosis affecting humans and hares in France. We describe the results of surveillance in both species, in 2007 and 2008.

Methods

Human tularemia cases are mandatorily notifiable in France since 2003. In hares, surveillance relies on volunteer hunter associations in all districts of the country. Data from mandatory reports and volunteer surveillance in 2007/2008 were analyzed and compared with previous results.

Results

In 2007/2008, 144 cases were reported in humans and 117 cases in hares. This was a 100% increase compared to previous years. Human cases differed from those of previous years only by the frequency of contact with breeding animals. Human cases without any documented risk exposure were also more frequent.

Conclusion

An increase of tularemia cases occurred in 2007/2008 in both species. Complementary studies are needed to identify the species reservoir in France to understand the causes of this peak of cases.     

深圳公立医院管理体制改革制度设计

深圳公立医院管理体制改革实行政事分开、管办分开,在理事会架构下按法定机构模式组建市医管中心,落实公立医院运营管理自主权.作者从当前公立医院管理体制的弊端入手,介绍了深圳市进行公立医院管理体制改革的基本思路及改革方案设计的主要举措,深入剖析了的改革方案的特点,并对改革效果进行了预测.     

Effects of nitrogen dioxide on red blood cells of rats: Changes in components of red cell membranes during in vivo exposure to NO2

Red cell membranes, prepared from red blood cells of rats exposed to 4, 10, or 20 ppm nitrogen dioxide (NO₂) for 1 to 10 days, were examined for evidence of changes in membrane components. Appreciable changes were not found in contents of phospholipid and cholesterol during exposure to 10 ppm NO₂. By contrast, protein content altered with the time of exposure. Moreover, changes in protein composition were observed by employing sodium dodecyl sulfate — polyacrylamide gel electrophoresis. Twenty-four-hour exposure to NO₂ at the concentration above 10 ppm resulted in a marked increase in the percentage of lysophosphatidylethanolamine (LysoPE) to the total phospholipids. The prolonged exposure to 10 ppm NO₂ gave rise to a further increase in LysoPE, whereas the percentage of phosphatidylethanolamine (PE) showed a gradual decrease. A 1-day exposure to 4.0 ppm NO₂ also caused an increase in sialic acid content and decreases in those of PE and hexose. In addition to contents of these components the percentage of LysoPE increased 5 days after exposure and the elevated values were maintained up to the end of exposure period. These results demonstrate that red blood cells in circulation exhibit different membrane properties in terms of lipid and carbohydrate composition during 10 days of exposure to 4.0 ppm NO₂.     

Fatigue and health in a seafaring population

Background Occupational fatigue is relatively common withinthe general population and has been linked to reduced performance,injury and longer term ill-health. Despite growing acknowledgementof this problem in the maritime sector, little research hasbeen conducted into the risk factors, prevalence and consequencesof seafarers' fatigue. Aims To examine the prevalence of fatigue among seafarers, identifypotential risk factors and assess possible links with poor performanceand ill-health. Methods Cross-sectional questionnaire survey of seafarers workingin the offshore oil support, short-sea and deep-sea shippingindustries. A number of tools were used including the fatiguesubscale of the profile of fatigue-related symptoms, the CognitiveFailures Questionnaire, the General Health Questionnaire andthe SF36 General Health scale. Results In all, 1855 questionnaires were completed giving anoverall response rate of 20%. Fatigue symptoms were associatedwith a range of occupational and environmental factors, manyunique to seafaring. Reporting a greater number of risk factorswas associated with greater fatigue [e.g. OR = 2.53 (1.90–3.35)for those with three or four risk factors and OR = 9.54 (6.95–13.09)for those with five or more risk factors]. There was also astrong link between fatigue and poorer cognitive and healthoutcomes, with fatigue the most important of a number of riskfactors, accounting for 10–14% of the variance. Conclusions Seafarers' fatigue could impact on safety withinthe industry and may be linked to longer term individual ill-health.It can only be addressed by considering how multiple factorscombine to contribute to fatigue.     

Occupational health hazards in mining: an overview

This review article outlines the physical, chemical, biological, ergonomic and psychosocial occupational health hazards of mining and associated metallurgical processes. Mining remains an important industrial sector in many parts of the world and although substantial progress has been made in the control of occupational health hazards, there remains room for further risk reduction. This applies particularly to traumatic injury hazards, ergonomic hazards and noise. Vigilance is also required to ensure exposures to coal dust and crystalline silica remain effectively controlled.