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. (TROX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Tronox produces and markets titanium dioxide. The stock also earns F’s in Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth. For more information, get Portfolio Grader’s complete analysis of TROX stock.

This week, Calgon Carbon Corporation (CCC) drops from a C to a D rating. Calgon Carbon is engaged in products and services for purifying water and air. For a full analysis of CCC stock, visit Portfolio Grader.

Rockwood Holdings, Inc. (ROC) is having a tough week. The company’s rating falls from a C to a D. 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. The stock price has fallen 8.6% over the past month, worse than the 1.7% decrease the S&P 500 has seen over the same period of time. To get an in-depth look at ROC, get Portfolio Grader’s complete analysis of ROC stock.

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.