For the current week, the overall ratings of three chemicals stocks are worse, according to the Portfolio Graderdatabase. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Tronox Ltd.’s (TROX) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Tronox produces and markets titanium dioxide. In Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth, TROX also gets F’s. To get an in-depth look at TROX, get Portfolio Grader’s complete analysis of TROX stock.

This is a rough week for Calgon Carbon Corporation (CCC). The company’s rating falls to D from the previous week’s C. Calgon Carbon is engaged in products and services for purifying water and air. Shares of the stock have been exchanging at an usually rapid pace, twice the rate of the week prior. The stock currently has a trailing PE Ratio of 25.50. For more information, get Portfolio Grader’s complete analysis of CCC stock.

This week, Rockwood Holdings, Inc. (ROC) drops from a C to a D rating. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. At $70.38, the stock is below the 50-day moving average of $74.36. For a full analysis of ROC stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.